xfs: remove xfs_inew_wait

With the remove of xfs_dqrele_all_inodes, xfs_inew_wait and all the
infrastructure used to wake the XFS_INEW bit waitqueue is unused.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 777eb1fa ("xfs: remove xfs_dqrele_all_inodes")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>