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

src/x64/assembler-x64.cc

Index: src/x64/assembler-x64.cc
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 9a0d18e9c2fba4c71648b999eb560165927ddbf9..45380465d4b8e42dd479e36ece009ef9efcbf826 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -1586,13 +1586,6 @@
   emit_operand(dst, src);
 }
 
-void Assembler::movsxbq(Register dst, Register src) {
-  EnsureSpace ensure_space(this);
-  emit_rex_64(dst, src);
-  emit(0x0F);
-  emit(0xBE);
-  emit_modrm(dst, src);
-}
 
 void Assembler::movsxwl(Register dst, Register src) {
   EnsureSpace ensure_space(this);
@@ -1620,13 +1613,6 @@
   emit_operand(dst, src);
 }
 
-void Assembler::movsxwq(Register dst, Register src) {
-  EnsureSpace ensure_space(this);
-  emit_rex_64(dst, src);
-  emit(0x0F);
-  emit(0xBF);
-  emit_modrm(dst, src);
-}
 
 void Assembler::movsxlq(Register dst, Register src) {
   EnsureSpace ensure_space(this);