👩‍🌾 Remove bitbucket-pipelines

[chapulina]

🦟 Bug fix

Fixes gazebo-tooling/release-tools#203

Summary

This will make CI run using Bionic for this branch, instead of Xenial, which is EOL.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

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https://github.com/osrf/buildfarmer/issues/224

[chapulina]

FYI, I updated the branch protections for ign-msgs[0-4] (i.e. pre-Citadel):

• Don't require Focal, because that's not supported
• Don't require Ubuntu, because there are unaddressed warnings

[caguero]

For some reasons, there are a bunch of new warnings...

[chapulina]

For some reasons, there are a bunch of new warnings...

This is targeting ign-msgs1, which is the version used by Gazebo 9. I think we probably never cleaned up warnings for this branch, and I'm not sure if we want to put time into it now, so I just relaxed the branch protections for now.