Remove Google Code importer

Google Code project hosting was shut down in 2016. GitLab is no longer seeing any import traffic from Google Code and will, therefore, retire the support for direct imports from Google Code.

Current state

https://gitlab.com/import/google_code/new

Desired state

The import option is no longer there and all associated code and documentation has been removed.

Todo

• Remove the frontend code
• Remove the backend code
• Remove the documentation
• Close the related issue