Revert "loop: cleanup partitions when detaching loop device"

Revert "loop: cleanup partitions when detaching loop device"

This reverts commit 0f425cc843419f0e9e83b3cee690fd6400e6a925.

There are situations where the destruction path is called
with the bdev->bd_mutex already held, which then deadlocks in
loop_clr_fd(). The normal partition cleanup does a trylock()
on the mutex, but it'd be nice to have a more bullet proof
method in loop. So punt this more involved fix to the next
merge window, and just back out this buggy fix for now.

Signed-off-by: Jens Axboe <axboe@kernel.dk>