EmbeddedVector lives on the stack only, and should not be implicitly
copied or assigned.
This also removes remaining uses of the removed Vector::set_start
method.

R=sigurds@chromium.org

Bug: v8:9142
Change-Id: I829e6ffad6b1a30baa6c874265e92d615dd0c981
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1578458Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60940}