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/hprof/hprof.cc b/runtime/hprof/hprof.cc
index c9e8426..dc42cfa 100644
--- a/runtime/hprof/hprof.cc
+++ b/runtime/hprof/hprof.cc
@@ -718,7 +718,7 @@
           source_file = "";
         }
         __ AddStringId(LookupStringId(source_file));
-        auto class_result = classes_.find(method->GetDeclaringClass());
+        auto class_result = classes_.find(method->GetDeclaringClass().Ptr());
         CHECK(class_result != classes_.end());
         __ AddU4(class_result->second);
         __ AddU4(frame->ComputeLineNumber());