ocfs2: remove unused ocfs2_handle_add_lock()

This gets us rid of a slab we no longer need, as well as removing the
majority of what's left on ocfs2_journal_handle.

ocfs2_commit_unstarted_handle() has no more real work to do, so remove that
function too.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>