LU-155 cleanup some dead code

LU-155 cleanup some dead code

- 2.x does not support any kernels with vfs intents, so we can drop the related lustre code
 (as a side note, HAVE_VFS_INTENT_PATCHES seems to be gone already)
- remove ll_pin/unpin since it won't be used any more
- add a comment to ll_ddelete()

Change-Id: I3ed16d84c8618071ea66d9c2cc9d2810b23f1830
Signed-off-by: Johann Lombardi <johann@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/359
Tested-by: Hudson
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Mikhail Pershin <tappro@whamcloud.com>