Remove deprecated use of cirq.google in install guide

[amcnamara]

Very minor fix. The install guide at https://quantumai.google/cirq/install has a validation step that references cirq.google which is a deprecated usage on new installs, example:

[amcnamara] > python -c 'import cirq; print(cirq.google.Foxtail)'
<string>:1: DeprecationWarning: cirq.google was used but is deprecated.
 it will be removed in cirq v0.14.
 Use cirq_google instead.

(0, 0)───(0, 1)───(0, 2)───(0, 3)───(0, 4)───(0, 5)───(0, 6)───(0, 7)───(0, 8)───(0, 9)───(0, 10)
│        │        │        │        │        │        │        │        │        │        │
│        │        │        │        │        │        │        │        │        │        │
(1, 0)───(1, 1)───(1, 2)───(1, 3)───(1, 4)───(1, 5)───(1, 6)───(1, 7)───(1, 8)───(1, 9)───(1, 10)
[amcnamara] > python -c 'import cirq_google; print(cirq_google.Foxtail)'
(0, 0)───(0, 1)───(0, 2)───(0, 3)───(0, 4)───(0, 5)───(0, 6)───(0, 7)───(0, 8)───(0, 9)───(0, 10)
│        │        │        │        │        │        │        │        │        │        │
│        │        │        │        │        │        │        │        │        │        │
(1, 0)───(1, 1)───(1, 2)───(1, 3)───(1, 4)───(1, 5)───(1, 6)───(1, 7)───(1, 8)───(1, 9)───(1, 10)

[amcnamara]

Looks like there are a few other references to cirq.google in the docs:

[amcnamara] > grep cirq\\.google -ir docs
docs/google/specification.md:This specification is defined in the Device proto within `cirq.google.api.v2`.
docs/google/specification.md:engine = cirq.google.Engine(project_id='your_project_id')
docs/google/specification.md:The `cirq.google.SerializableDevice` class allows someone to take this
docs/google/specification.md:The `cirq.google.SerializableDevice` combines a `DeviceSpecification` protocol
docs/google/specification.md:import cirq.google as cg
docs/google/specification.md:                   proto_version=cirq.google.ProtoVersion.V2)
docs/google/engine.md:the only supported client for this API, using the `cirq.google.Engine` class.
docs/google/engine.md:engine = cirq.google.Engine(.*)
docs/google/engine.md:import cirq.google as cg
docs/google/engine.md:Several public devices have been released and can be found in the `cirq.google`
docs/google/engine.md:into a `cirq.Device` by using `cirq.google.SerializableDevice.from_proto()` that will
docs/google/engine.md:engine = cirq.google.Engine(project_id='YOUR_PROJECT_ID')
docs/google/engine.md:                       gate_set=cirq.google.FSIM_GATESET,
docs/google/engine.md:engine = cirq.google.Engine(project_id='YOUR_PROJECT_ID')
docs/google/engine.md:To list the executions of your circuit, i.e. the jobs, you can use `cirq.google.Engine.list_jobs()`.
docs/google/engine.md:from cirq.google.engine.client.quantum import enums
docs/google/engine.md:engine = cirq.google.Engine(project_id='YOUR_PROJECT_ID')
docs/google/engine.md:To list the different instances of your circuits uploaded, i.e. the programs, you can use `cirq.google.Engine.list_programs()`.
docs/google/engine.md:With an existing `cirq.google.EngineProgram` object, you can list any jobs that were run using that program.
docs/google/engine.md:from cirq.google.engine.client.quantum import enums
docs/google/engine.md:engine = cirq.google.Engine(project_id='YOUR_PROJECT_ID')
docs/google/devices.md:cirq.Z(cirq.GridQubit(5, 5)).with_tags(cirq.google.PhysicalZTag())
docs/google/devices.md:be accessed using `cirq.google.SYC`.  This gate is equivalent to
docs/google/devices.md:This gate has a duration of 12ns and can be used in `cirq.google.SYC_GATESET`
docs/google/devices.md:or in the `cirq.google.FSIM_GATESET`.
docs/google/devices.md:`cirq.google.SQRT_ISWAP_GATESET` or in the `cirq.google.FSIM_GATESET`.
docs/google/devices.md:It can be accessing by using `cirq.google.Sycamore`. This device has two possible
docs/google/devices.md:used on `cirq.google.optimized_for_sycamore` with optimizer type `sqrt_iswap`
docs/google/devices.md:*  Sycamore gate. This gate, equivalent to FSimGate(π/2, π/6) can be used as `cirq.google.SYC`
docs/google/devices.md:by using `cirq.google.optimized_for_sycamore` with optimizer type `sycamore`
docs/google/devices.md:This grid can be accessed using `cirq.google.Sycamore23` and uses the same gate sets and
docs/google/devices.md:It can be accessing by using `cirq.google.Bristlecone`. Circuits can be compiled to it by using
docs/google/devices.md:`cirq.google.optimized_for_xmon` or by using `cirq.google.optimized_for_sycamore` with
docs/google/devices.md:It can be accessing by using `cirq.google.Foxtail`. Circuits can be compiled to it by using
docs/google/devices.md:`cirq.google.optimized_for_xmon` or by using `cirq.google.optimized_for_sycamore` with
docs/google/calibration.md:import cirq.google as cg
docs/install.md:    python -c 'import cirq; print(cirq.google.Foxtail)'
docs/install.md:    python -c 'import cirq; print(cirq.google.Foxtail)'
docs/install.md:    python -c "import cirq; print(cirq.google.Foxtail)"
docs/dev/notebooks.md:Unfortunately we have no easy way to test notebooks with external API dependencies, e.g. cirq.google's Engine API.
docs/dev/development.md:        print(cirq.google.Foxtail)
docs/dev/development.md:    python -c "import cirq; print(cirq.google.Foxtail)"

I'm happy to go through these individually and verify they all match up with the new module if that's useful, but it'll take a while.

[MichaelBroughton]

LGTM.

but it'll take a while.

In that case I may do a follow up so we spend as few days as possible with broken docs.