This function was only used in a single test, and it tests a scenario
which cannot happen any more with the module cache: Having two copies of
the same NativeModule in an isolate.

Hence remove the respective runtime function and the test.

R=ahaas@chromium.org

Change-Id: Id7cdffbdf1bdf95a7eb31fdeb7d75b8e326bb90e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2339100Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69246}