UPSTREAM: task_work: remove legacy TWA_SIGNAL path

[ Upstream commit 03941ccfda161c2680147fa5ab92aead2a79cac1 ]

All archs now support TIF_NOTIFY_SIGNAL.

Change-Id: I3fc938645ac7be18300432713909ccfaa7cd2711
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 61bdeb142e8f7550826373295cb35b3571d70f62)
Bug: 268174392
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>