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/monitor.cc b/runtime/monitor.cc
index 2a938da..e110763 100644
--- a/runtime/monitor.cc
+++ b/runtime/monitor.cc
@@ -140,7 +140,7 @@
     }
   }
   DCHECK(HasHashCode());
-  return hash_code_.LoadRelaxed();
+  return hash_code_.load(std::memory_order_relaxed);
 }
 
 bool Monitor::Install(Thread* self) {
@@ -155,7 +155,7 @@
       break;
     }
     case LockWord::kHashCode: {
-      CHECK_EQ(hash_code_.LoadRelaxed(), static_cast<int32_t>(lw.GetHashCode()));
+      CHECK_EQ(hash_code_.load(std::memory_order_relaxed), static_cast<int32_t>(lw.GetHashCode()));
       break;
     }
     case LockWord::kFatLocked: {