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/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index 70af49f..f493b66 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -2268,7 +2268,7 @@
       ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
       PointerSize image_size = class_linker->GetImagePointerSize();
       HInvokeStaticOrDirect* invoke = instruction->AsInvokeStaticOrDirect();
-      mirror::Class* system = invoke->GetResolvedMethod()->GetDeclaringClass();
+      ObjPtr<mirror::Class> system = invoke->GetResolvedMethod()->GetDeclaringClass();
       ArtMethod* method = nullptr;
       switch (source_component_type) {
         case DataType::Type::kBool:
diff --git a/compiler/optimizing/reference_type_propagation.cc b/compiler/optimizing/reference_type_propagation.cc
index f3fe625..0d62248 100644
--- a/compiler/optimizing/reference_type_propagation.cc
+++ b/compiler/optimizing/reference_type_propagation.cc
@@ -563,7 +563,7 @@
       ArtMethod* method = cl->ResolveMethod<ClassLinker::ResolveMode::kNoChecks>(
           dex_method_index, dex_cache, loader, /* referrer */ nullptr, kDirect);
       DCHECK(method != nullptr);
-      mirror::Class* declaring_class = method->GetDeclaringClass();
+      ObjPtr<mirror::Class> declaring_class = method->GetDeclaringClass();
       DCHECK(declaring_class != nullptr);
       DCHECK(declaring_class->IsStringClass())
           << "Expected String class: " << declaring_class->PrettyDescriptor();
@@ -572,7 +572,7 @@
     }
     instr->SetReferenceTypeInfo(
         ReferenceTypeInfo::Create(handle_cache_->GetStringClassHandle(), /* is_exact */ true));
-  } else if (IsAdmissible(klass.Ptr())) {
+  } else if (IsAdmissible(klass)) {
     ReferenceTypeInfo::TypeHandle handle = handle_cache_->NewHandle(klass);
     is_exact = is_exact || handle->CannotBeAssignedFromOtherTypes();
     instr->SetReferenceTypeInfo(ReferenceTypeInfo::Create(handle, is_exact));