This removes the low-level {SwitchMemoryPermissionsToWritable()} and
{SwitchMemoryPermissionsToExecutable()} functions. They are only used in
tests and can be replaced by {CodeSpaceWriteScope} objects that we also
use in production.

R=jkummerow@chromium.org

Change-Id: I7ba702c836f3ac2dd7c7a81d6362040b28e8bef4
Cq-Include-Trybots: luci.v8.try:v8_mac_arm64_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_mac_arm64_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3024150
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75739}