xfs: fold xfs_attr_remove_int into xfs_attr_remove

Also remove a useless ilock roundtrip for the first attr fork check, it's
racy anyway and we redo it later under the ilock before we start the removal.

Plus various minor style fixes to the new xfs_attr_remove.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>