mtip32xx: remove trim support

The trim support in mtip32xx has been "temporarily" disabled for 6
years, which is 3/4 of the time the driver even exists in the tree.

Remove it as it obviously is dead code now.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>