xfs: Merge xfs_delattr_context into xfs_attr_item

xfs: Merge xfs_delattr_context into xfs_attr_item

Source kernel commit: d68c51e9a4095b57f06bf5dd15ab8fae6dab5d8b

This is a clean up patch that merges xfs_delattr_context into
xfs_attr_item.  Now that the refactoring is complete and the delayed
operation infrastructure is in place, we can combine these to eliminate
the extra struct

Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>