phabsend: make --amend the default The local tag feature was intended to make `phabsend` closer to `email` workflow. But its experience is not great in multiple ways: - after rebase, obsoleted changesets are still visible because of tags - without obsstore, the association information will get lost - even with obsstore, things could go wrong with graft, export+import - no easy way to tell which Differential Revision a commit is associated Therefore make `--amend` the default. People wanting the old behavior can use `--no-amend`. Differential Revision: https://phab.mercurial-scm.org/D511