[d8] Avoid printing unhandled rejected Promises in Shell::RunMain

This simplification helps with correctness fuzzers where Promises
created during error printing are flakily handled.

We might skip over certain rejected Promises that were created after
finishing running the script. This seems to be a reasonable compromise
in helping debugging scripts with unhandled rejections in d8.

Bug: chromium:1126309
Change-Id: Ia87c80cfd390bf8c6a724dc2f0e9e5fd1599e332
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2460814Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70410}

src/d8/d8.cc

@@ -3572,7 +3572,6 @@ int Shell::RunMain(Isolate* isolate, bool last_run) {
       PerIsolateData::RealmScope realm_scope(PerIsolateData::Get(isolate));
       if (!options.isolate_sources[0].Execute(isolate)) success = false;
       if (!CompleteMessageLoop(isolate)) success = false;
-      if (!HandleUnhandledPromiseRejections(isolate)) success = false;
     }
     if (!use_existing_context) {
       DisposeModuleEmbedderData(context);