drm/nouveau/therm: remove ineffective workarounds for alarm bugs

commit e4311ee5 upstream.

These were ineffective due to touching the list without the alarm lock,
but should no longer be required.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>