Revert "mm: add /proc controls for pdflush threads"

Revert "mm: add /proc controls for pdflush threads"

This reverts commit 106fc7b37938e6b5a68476d34f1c0f5eafccd461.

Work is progressing to switch away from pdflush as the process backing
for flushing out dirty data. So it seems pointless to add more knobs
to control pdflush threads. The original author of the patch did not
have any specific use cases for adding the knobs, so we can easily
revert this before 2.6.30 to avoid having to maintain this API
forever.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>