Part of ongoing work to remove the construct_stub.

For non-constructable functions, don't use the non-constructable stub,
instead handle non-constructables explicitly in ConstructFunction.

Bug: v8:7503
Change-Id: I24aa7c2d5e934d5e80cd96afaf005342773d57af
Reviewed-on: https://chromium-review.googlesource.com/975961
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52185}