Revert of [Atomics] Remove Atomics code stubs; use TF ops

src/compiler/machine-operator.h

Index: src/compiler/machine-operator.h
diff --git a/src/compiler/machine-operator.h b/src/compiler/machine-operator.h
index 8e43f48042ed18456e5c47ffe07914729b039e1c..68e393aaddf74fbbf650fb87a9b66c2400406eac 100644
--- a/src/compiler/machine-operator.h
+++ b/src/compiler/machine-operator.h
@@ -335,9 +335,6 @@
   // checked-store heap, index, length, value
   const Operator* CheckedStore(CheckedStoreRepresentation);
 
-  // atomic-load [base + index]
-  const Operator* AtomicLoad(LoadRepresentation rep);
-
   // Target machine word-size assumed by this builder.
   bool Is32() const { return word() == MachineRepresentation::kWord32; }
   bool Is64() const { return word() == MachineRepresentation::kWord64; }