Revert "bcache: ignore pending signals when creating gc and allocator thread"

Revert "bcache: ignore pending signals when creating gc and allocator thread"

This reverts commit c3daa416b4100958e4a798c68df19df9c5b3d40e.

We can't just go flushing random signals, under the assumption that the
OOM killer will just do something else. It's not safe from the OOM
perspective, and it could also cause other signals to get randomly lost.

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