xfs: do not take the iolock in xfs_inactive

An inode that enters xfs_inactive has been removed from all global
lists but the inode hash, and can't be recycled in xfs_iget before
it has been marked reclaimable.  Thus taking the iolock in here
is not nessecary at all, and given the amount of lockdep false
positives it has triggered already I'd rather remove the locking.

The only change outside of xfs_inactive is relaxing an assert in
xfs_itruncate_extents.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>