[Fix] Fix TestMissingAbstractMethodImpl

Summary:
My previous fix for nemo broke one of the QuickTests, that was expecting a
CodeError even in the presence of redeclared base classes.

I've changed the test so that we shouldnt generate a error, and made it check
for that.

Test Plan: fast_tests

Reviewers: qigao, myang

Reviewed By: qigao

CC: ps, mwilliams, qigao

Differential Revision: 341490

src/test/test_code_error.cpp

@@ -374,15 +374,14 @@ bool TestCodeError::TestMissingAbstractMethodImpl() {
      "}"
      "class B implements A {"
      "}");
-  VE(MissingAbstractMethodImpl,
+  VEN(MissingAbstractMethodImpl,
      "<?php "
      "if (true) {"
      "  abstract class A {"
      "    abstract function foo();"
      "  }"
      "} else {"
      "  abstract class A {"
-     "    abstract function foo();"
      "  }"
      "}"
      "class B extends A {"