[x64] Removed unused atomic instruction-codes

These are never generated by the instruction-selector, and don't need to
be defined.

Bug: v8:11074
Change-Id: I83a5760b6350155fd19d069be6aeeec5887e5880
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2643396Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72237}

src/compiler/backend/x64/code-generator-x64.cc

@@ -4313,14 +4313,6 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleArchInstruction(
     case kWord32AtomicStoreWord8:
     case kWord32AtomicStoreWord16:
     case kWord32AtomicStoreWord32:
-    case kX64Word64AtomicLoadUint8:
-    case kX64Word64AtomicLoadUint16:
-    case kX64Word64AtomicLoadUint32:
-    case kX64Word64AtomicLoadUint64:
-    case kX64Word64AtomicStoreWord8:
-    case kX64Word64AtomicStoreWord16:
-    case kX64Word64AtomicStoreWord32:
-    case kX64Word64AtomicStoreWord64:
       UNREACHABLE();  // Won't be generated by instruction selector.
       break;
   }

src/compiler/backend/x64/instruction-codes-x64.h

@@ -389,14 +389,6 @@ namespace compiler {
   V(X64V16x8AllTrue)                      \
   V(X64V8x16AnyTrue)                      \
   V(X64V8x16AllTrue)                      \
-  V(X64Word64AtomicLoadUint8)             \
-  V(X64Word64AtomicLoadUint16)            \
-  V(X64Word64AtomicLoadUint32)            \
-  V(X64Word64AtomicLoadUint64)            \
-  V(X64Word64AtomicStoreWord8)            \
-  V(X64Word64AtomicStoreWord16)           \
-  V(X64Word64AtomicStoreWord32)           \
-  V(X64Word64AtomicStoreWord64)           \
   V(X64Word64AtomicAddUint8)              \
   V(X64Word64AtomicAddUint16)             \
   V(X64Word64AtomicAddUint32)             \

src/compiler/backend/x64/instruction-scheduler-x64.cc

@@ -420,16 +420,6 @@ int InstructionScheduler::GetTargetInstructionFlags(
     case kX64LFence:
       return kHasSideEffect;
 
-    case kX64Word64AtomicLoadUint8:
-    case kX64Word64AtomicLoadUint16:
-    case kX64Word64AtomicLoadUint32:
-    case kX64Word64AtomicLoadUint64:
-      return kIsLoadOperation;
-
-    case kX64Word64AtomicStoreWord8:
-    case kX64Word64AtomicStoreWord16:
-    case kX64Word64AtomicStoreWord32:
-    case kX64Word64AtomicStoreWord64:
     case kX64Word64AtomicAddUint8:
     case kX64Word64AtomicAddUint16:
     case kX64Word64AtomicAddUint32: