xfs: remove xfs_trans_ail_delete_bulk

xfs_iflush_done uses an on-stack variable length array to pass the log
items to be deleted to xfs_trans_ail_delete_bulk.  On-stack VLAs are a
nasty gcc extension that can lead to unbounded stack allocations, but
fortunately we can easily avoid them by simply open coding
xfs_trans_ail_delete_bulk in xfs_iflush_done, which is the only caller
of it except for the single-item xfs_trans_ail_delete.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>