Remove unnecessary and expensive hasService check

[tfrommen]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

This PR removes the ContainerConfigurator::hasService check inside ContainerConfigurator::addService.

This is unnecessary and potentially expensive (especially with large and/or multiple and/or composite containers).

Previously, there was an exception thrown in case someone wanted to register a module with an existing ID. In 74cf1a5, the exception has been removed (for the reasons mentioned in #17).

This means, previously, we needed to know if there already is a service with the given ID. Now, we don't care, and we can simply unset the potentially-existing service as unset($foo) does not care whether $foo exists.

What is the current behavior? (You can also link to an open issue here)

Calling ContainerConfigurator::addService will internally call ContainerConfigurator::hasService.

What is the new behavior (if this is a feature change)?

Calling ContainerConfigurator::addService will attempt to unset the entry in the factory lookup table without checking if it exists first.

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

Other information:

[Biont]

The explanation makes sense to me. LGTM, thanks