The only opcode which can pop the last control block is "end".
There is already validation in place to check that no code is following
the last "end". Thus all checks for a non-empty control stack in other
opcodes are redundant and can be replaced by DCHECKs.

Drive-by: Avoid the use of {PushControl} for pushing the very first
block, to avoid another check for an empty control stack there.

R=thibaudm@chromium.org

Change-Id: I8f04b225a61f832bca2dd7b706e31d1faa173767
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2678162Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72589}