Remove out-dated ExternalReference cctest

Change-Id: I1944a179131af2027bd69a4e39e0c4e0eafb1a65
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3820582
Commit-Queue: Darius Mercadier <dmercadier@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82326}

test/cctest/test-serialize.cc

@@ -3342,6 +3342,9 @@ UNINITIALIZED_TEST(SnapshotCreatorDuplicateFunctions) {
   FreeCurrentEmbeddedBlob();
 }
 
+#ifndef V8_SHARED_RO_HEAP
+// We do not support building multiple snapshots when read-only heap is shared.
+
 TEST(SnapshotCreatorNoExternalReferencesCustomFail1) {
   DisableAlwaysOpt();
   v8::StartupData blob = CreateSnapshotWithDefaultAndCustom();
@@ -3392,6 +3395,8 @@ TEST(SnapshotCreatorNoExternalReferencesCustomFail2) {
   delete[] blob.data;
 }
 
+#endif  // V8_SHARED_RO_HEAP
+
 UNINITIALIZED_TEST(SnapshotCreatorUnknownExternalReferences) {
   DisableAlwaysOpt();
   DisableEmbeddedBlobRefcounting();