ART: Simplify atomic.h

Prefer std::atomic operations over wrappers in atomic.h. Exceptions
are cases that relate to the Java data memory operations and CAS
operations.

Bug: 71621075
Test: art/test.py --host -j32
Test: art/test.py --target --64 -j4
Change-Id: I9a157e9dede852c1b2aa67d22e3e604a68a9ef1c
diff --git a/runtime/class_table-inl.h b/runtime/class_table-inl.h
index c59e2e8..5da5470 100644
--- a/runtime/class_table-inl.h
+++ b/runtime/class_table-inl.h
@@ -88,7 +88,7 @@
 
 template<ReadBarrierOption kReadBarrierOption>
 inline mirror::Class* ClassTable::TableSlot::Read() const {
-  const uint32_t before = data_.LoadRelaxed();
+  const uint32_t before = data_.load(std::memory_order_relaxed);
   ObjPtr<mirror::Class> const before_ptr(ExtractPtr(before));
   ObjPtr<mirror::Class> const after_ptr(
       GcRoot<mirror::Class>(before_ptr).Read<kReadBarrierOption>());
@@ -102,7 +102,7 @@
 
 template<typename Visitor>
 inline void ClassTable::TableSlot::VisitRoot(const Visitor& visitor) const {
-  const uint32_t before = data_.LoadRelaxed();
+  const uint32_t before = data_.load(std::memory_order_relaxed);
   ObjPtr<mirror::Class> before_ptr(ExtractPtr(before));
   GcRoot<mirror::Class> root(before_ptr);
   visitor.VisitRoot(root.AddressWithoutBarrier());