Remove monotonic and absolute metrics intrument options

[mauriciovasquezbernal]

Fixes #404.

Following the spec open-telemetry/opentelemetry-specification#430.

Just some cleanup before implementing other things in the metrics.

[codecov-io]

Codecov Report

Merging #410 into master will decrease coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #410      +/-   ##
==========================================
- Coverage   85.85%   85.76%   -0.09%     
==========================================
  Files          41       41              
  Lines        2078     2065      -13     
  Branches      242      239       -3     
==========================================
- Hits         1784     1771      -13     
  Misses        223      223              
  Partials       71       71

Impacted Files	Coverage Δ
...elemetry-api/src/opentelemetry/metrics/__init__.py	95.58% <ø> (ø)	⬆️
...etry-sdk/src/opentelemetry/sdk/metrics/__init__.py	98.29% <ø> (-0.18%)	⬇️

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[hectorhdzg]

LGTM, Monotonicity support will be discussed and added at later time, currently in Future Work: Option Support in the spec

[c24t]

No reason to hold this up, but note that we'll need input validation when we have default aggregators for both counter and measure instruments.