This patch removes the NumberConstructor_ConstructStub builtin,
merging its functionality into the refactored NumberConstructor
TurboFan builtin.

This brings us closer to our goal of deprecating the `construct_stub`
field in `SharedFunctionInfo`.

Bug: v8:7503, v8:7518
Change-Id: Ia407a2d43cda9fc7b26e13274fd79f110b6232ca
Reviewed-on: https://chromium-review.googlesource.com/946008
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51694}