Since the interpreter is only used for internal testing now, it does not
have an associated frame type any more. We thus cannot call external
functions any more, since a stack walk would not know how to handle
interpreter frames.

All code for calling external (imported) functions is dead by now, so
this CL removes it.

R=thibaudm@chromium.org

Bug: v8:10389
Change-Id: If4b56b93e63002a1e5463f278f0271eb413762eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2218287
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68039}