Remove Google Chat/Hangouts integration

[frenck]

Breaking change

The Google Chat integration has been removed. It relied on the Google Hangouts APIs, which have been shut down, rendering the integration unusable.

Proposed change

See #82235

The Google Hangouts endpoints, used by the Google Chat integration (unfortunately named), have been shut down. While Google Chat still exists, Hangouts no longer does. This integration, in its current state, is no longer able to function.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: closes Google Chat integration has stopped working #82235
• This PR is related to issue:
• Link to documentation pull request: Remove Google Chat/Hangouts integration home-assistant.io#25043
• Link to brands pull request: Remove Google Chat/Hangouts integration brands#3880

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

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• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.
• Untested files have been added to .coveragerc.

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