Revert -Wunreachable-code workaround.

Bug: http://b/31104323
Test: Built/ran ART successfully on sailfish.

This reverts commit 813b9c47d8952b3f02a6032d79d66433c981d030, which
added a workaround for Clang mistriggering -Wunreachable-code.

Change-Id: I46636c9b4f574a870c1f95b6160d05f2a75f8ab8
diff --git a/runtime/class_table.cc b/runtime/class_table.cc
index ff846a7..f1458b4 100644
--- a/runtime/class_table.cc
+++ b/runtime/class_table.cc
@@ -55,10 +55,6 @@
   return nullptr;
 }
 
-// Bug: http://b/31104323 Ignore -Wunreachable-code from the for loop below
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wunreachable-code"
-
 mirror::Class* ClassTable::UpdateClass(const char* descriptor, mirror::Class* klass, size_t hash) {
   WriterMutexLock mu(Thread::Current(), lock_);
   // Should only be updating latest table.
@@ -84,8 +80,6 @@
   return existing;
 }
 
-#pragma clang diagnostic pop  // http://b/31104323
-
 size_t ClassTable::CountDefiningLoaderClasses(ObjPtr<mirror::ClassLoader> defining_loader,
                                               const ClassSet& set) const {
   size_t count = 0;