Revert "[test] Update MakeExternal tests"

This reverts commit 37c3e05e.

Reason for revert: https://chromium-review.googlesource.com/c/v8/v8/+/2565511 has to be reverted, and this was a follow-up to that

Original change's description:
> [test] Update MakeExternal tests
>
> They weren't initializing the VM at the start of the test. Also updated
> the test description.
>
> Bug: v8:7790
> Change-Id: I7b9df9e3aebb43fc526e16ec260aa071c0fdeb92
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2615019
> Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71978}

TBR=leszeks@chromium.org,solanes@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:7790
Change-Id: I35bc0090c3beed4ef11a458f0e26c44b22f7b654
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2627606Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72114}

test/cctest/test-strings.cc

@@ -1948,10 +1948,9 @@ TEST(Regress876759) {
   CHECK(String::IsOneByteRepresentationUnderneath(*sliced));
 }
 
-// Show that small internal strings are not externalizable since it would make
-// them external and uncached through MakeExternal. One byte version.
+// Show failure when trying to create and internal, external and uncached string
+// through MakeExternal. One byte version.
 TEST(MakeExternalCreationFailureOneByte) {
-  CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   Factory* factory = isolate->factory();
 // Due to different size restrictions the string needs to be small but not too
@@ -1972,10 +1971,9 @@ TEST(MakeExternalCreationFailureOneByte) {
   CHECK(!one_byte_string->SupportsExternalization());
 }
 
-// Show that small internal strings are not externalizable since it would make
-// them external and uncached through MakeExternal. Two byte version.
+// Show failure when trying to create and internal, external and uncached string
+// through MakeExternal. Two byte version.
 TEST(MakeExternalCreationFailureTwoByte) {
-  CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   Factory* factory = isolate->factory();
   // Due to different size restrictions the string needs to be small but not too