Also make return and unconditional jumps kill the environment instead
of clearing it. This was still leftover from before we introduced
liveness and prevented sharing as well.

Bug: v8:7790
Change-Id: Ic79d64c9eaedf608d26e3265d4b27d21f7f3dfe1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1948710
Auto-Submit: Georg Neis <neis@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65345}