With `main` in convergence mode and no release branch active yet, the "Original
PR:" and "Reviewers:" fields of the pull request template are confusing because
they don't make sense for the vast majority of PRs. Once there is a release
branch that changes are being regularly cherry-picked to, the fields can be
added back on the release branch.
`swiftlang` now has an equivalent organization-wide PR template, so we
no longer need this local one. Also, prompt folks to use this template
when targeting a release branch in the default PR template.
Mishal Shah
Allan Shortlidge
Mishal Shah
Anthony Latsis