The test was explicitly tiering up or down a module, without respecting
other isolates. Thus it was failing in multi-isolate mode.
This CL removes two runtime functions which do not make sense in a
multi-isolate setting (and were only used in this one test), and
replaces them with runtime functions that mimic what enabling/disabling
the debugger domain does: As long as there is at least one isolate which
needs modules to be tiered down, we keep them tiered down.

R=thibaudm@chromium.org

Bug: v8:10359, v8:10099
Change-Id: Ia85f4ea29ba6a6bb54aca54a48fadd351121d3eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2637231Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72164}