ObjPtr<>-ify ArtMethod and mirror::Method.

And clean up some forgotten things after old CLs.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 31113334
Change-Id: I8af0e845c24d674d0efab21d80c29949b1cc0593
diff --git a/runtime/jni/check_jni.cc b/runtime/jni/check_jni.cc
index 7919c32..66bd74b 100644
--- a/runtime/jni/check_jni.cc
+++ b/runtime/jni/check_jni.cc
@@ -1286,7 +1286,7 @@
     }
     ArtMethod* m = jni::DecodeArtMethod(mid);
     // TODO: Better check here.
-    if (!Runtime::Current()->GetHeap()->IsValidObjectAddress(m->GetDeclaringClass())) {
+    if (!Runtime::Current()->GetHeap()->IsValidObjectAddress(m->GetDeclaringClass().Ptr())) {
       Runtime::Current()->GetHeap()->DumpSpaces(LOG_STREAM(ERROR));
       AbortF("invalid jmethodID: %p", mid);
       return nullptr;