The `FunctionTemplate::SetHiddenPrototype()` API was removed in a
previous CL, after being deprecated since beginning of the year. This
removes all the logic behind it, leaving us with just the special case
of the JSGlobalProxy which has the JSGlobalObject as its hidden prototype.

This gives us back one bit in `Map::bit_field2` and removes quite a bit
of complexity from the code base (especially due to previous work from
verwaest@ in this area).

Bug: v8:9267
Change-Id: Id04b59686212fe35a63c9451aa3e045f0766b9cc
Cq-Include-Trybots: luci.chromium.try:linux-rel,win7-rel
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1619752
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61938}