This method is rarely used, and has several problems:
1) It CHECKs that the value is not undefined, then creates a
   {Handle<T>} which again DCHECKs that the value is of type {T}.
2) It is called on a raw {FixedArray} but returns a handle.
3) It is often used when no handle is actually needed, adding
   unnecessary overhead.
4) It adds complexity and hides actual checks and handlification.

This CL removes that method, replacing some uses by explicit CHECKs (in
tests) and relying on the DCHECKs in the casts otherwise.

R=mstarzinger@chromium.org

Bug: v8:9183
Change-Id: I90ff59e8b78c909a9a207029d8cc9ab16c0c7b56
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1621939
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61710}