[XFS] kill usesless IHOLD calls in xfs_remove and xfs_rmdir

The VFS always has an inode reference when we call these functions. So we
only need to grab a signle reference to each inode that's joined to a
transaction - all the other bumping and dropping is as useless as the
comments describing the IRIX semantics.

SGI-PV: 976035
SGI-Modid: xfs-linux-melb:xfs-kern:30912a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>