We have the generic {no_reg} and {no_dreg}, other definitions are dead.
Currently even {no_dreg} is dead, but I am keeping this because I can
see future need for that.

R=mstarzinger@chromium.org

Bug: v8:8238
Change-Id: I0de597fead6b3def18fd5c530419d3c149f235a8
Reviewed-on: https://chromium-review.googlesource.com/1251123Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56288}