Remove discontinued GoogleOpenId backend

[andersk]

Proposed changes

The Google OpenID backend was discontinued on the server side in 2015, in favor of OpenID Connect (our GoogleOpenIdConnect backend).

https://support.google.com/accounts/answer/6206245

Fixes #462. Fixes #472.

This is needed to get Travis passing again.

Types of changes

Please check the type of change your PR introduces:

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (PEP8, lint, formatting, renaming, etc)
• Refactoring (no functional changes, no api changes)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Build related changes (build process, tests runner, etc)
• Other (please describe):

Checklist

Put an x in the boxes that apply. You can also fill these out after creating
the PR. If you're unsure about any of them, don't hesitate to ask. We're here to
help! This is simply a reminder of what we are going to look for before merging
your code.

• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works

Other information

Any other information that is important to this PR such as screenshots of how
the component looks before and after the change.

[nijel]

It certainly makes sense to drop this.

[yuekui]

It certainly makes sense to drop this.

Hi @nijel could you please help to merge this PR and also help to merge others as well? Thanks a lot! (some of the pending PRs were marked as stale and going to be closed without further action taken)

[nijel]

Sorry, I can't as I don't have write access to this repository. See #445