In most places we already call them "branches", and the spec also only
uses this name. Hence remove the remaining mentions of "break".

R=titzer@chromium.org

Bug: v8:8562
Change-Id: I64ac39324681b8214cd2e68315eb86a69d85cba8
Reviewed-on: https://chromium-review.googlesource.com/c/1371567Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58153}