libxfs: clean up remaining LIBXFS_MOUNT flags

libxfs: clean up remaining LIBXFS_MOUNT flags

Now that userspace libxfs also uses m_opstate to track operational
state, the LIBXFS_MOUNT_* flags are only used for the flags argument
passed to libxfs_mount().  Update the comment to reflect this, and clean
up the flags and function declaration whiel we're at it.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>