Merge branch 'js/retire-preserve-merges'

Merge branch 'js/retire-preserve-merges'

The "--preserve-merges" option of "git rebase" has been removed.

* js/retire-preserve-merges:
  sequencer: restrict scope of a formerly public function
  rebase: remove a no-longer-used function
  rebase: stop mentioning the -p option in comments
  rebase: remove obsolete code comment
  rebase: drop the internal `rebase--interactive` command
  git-svn: drop support for `--preserve-merges`
  rebase: drop support for `--preserve-merges`
  pull: remove support for `--rebase=preserve`
  tests: stop testing `git rebase --preserve-merges`
  remote: warn about unhandled branch.<name>.rebase values
  t5520: do not use `pull.rebase=preserve`