Revert of [x64] Zero/sign-extend loads to 64-bit registers.

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

Index: src/compiler/x64/code-generator-x64.cc
diff --git a/src/compiler/x64/code-generator-x64.cc b/src/compiler/x64/code-generator-x64.cc
index 2baf91367fa65a6350bc2155bd51ba397375f6f2..0ab84e412be54008c1cf154eee2c9c0a14eb480c 100644
--- a/src/compiler/x64/code-generator-x64.cc
+++ b/src/compiler/x64/code-generator-x64.cc
@@ -1737,14 +1737,6 @@
       ASSEMBLE_MOVX(movzxbl);
       __ AssertZeroExtended(i.OutputRegister());
       break;
-    case kX64Movsxbq:
-      ASSEMBLE_MOVX(movsxbq);
-      __ AssertZeroExtended(i.OutputRegister());
-      break;
-    case kX64Movzxbq:
-      ASSEMBLE_MOVX(movzxbq);
-      __ AssertZeroExtended(i.OutputRegister());
-      break;
     case kX64Movb: {
       size_t index = 0;
       Operand operand = i.MemoryOperand(&index);
@@ -1761,14 +1753,6 @@
       break;
     case kX64Movzxwl:
       ASSEMBLE_MOVX(movzxwl);
-      __ AssertZeroExtended(i.OutputRegister());
-      break;
-    case kX64Movsxwq:
-      ASSEMBLE_MOVX(movsxwq);
-      __ AssertZeroExtended(i.OutputRegister());
-      break;
-    case kX64Movzxwq:
-      ASSEMBLE_MOVX(movzxwq);
       __ AssertZeroExtended(i.OutputRegister());
       break;
     case kX64Movw: {