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 0b96da639a4874311e9b5156405f69ef9fc3bef8.

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>