refactor(android): cleanup obsolete code

[breautek]

Platforms affected

Android

Motivation and Context

Depends on #308

Improved maintenance

Description

Cleanup unused imports, redundant if conditions, and unused private methods.

Testing

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[erisu]

When squash merging, make sure the commit title contains the updated refactor(android):

I noticed the current commit title missing the platform as checklist requested:

Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))

[erisu]

Other then commit message, everything else looks good.