assistant, undo: When committing, let the usual git commit hooks run

assistant, undo: When committing, let the usual git commit hooks run

Was doing a Git.Branch.commit for historical reasons to do with direct
mode, which no longer apply.

Note that the preCommitAnnexHook is no longer called in commitStaged
because git-annex installs a pre-commit hook that runs the pre-commit-annex
hook. And git commit will run the pre-commit hook.

Sponsored-by: the NIH-funded NICEMAN (ReproNim TR&D3) project