Move movq(Register, ExternalReference) into X64 MacroAssembler

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index c715bcef96531429aa0ba2c1f897da424cf303c1..682432196617c32ae0c42c63c375b8a3cadbafa3 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -723,8 +723,6 @@ class Assembler : public AssemblerBase {
   // All 64-bit immediates must have a relocation mode.
   void movq(Register dst, void* ptr, RelocInfo::Mode rmode);
   void movq(Register dst, int64_t value, RelocInfo::Mode rmode);
-  // Moves the address of the external reference into the register.
-  void movq(Register dst, ExternalReference ext);
   void movq(Register dst, Handle<Object> handle, RelocInfo::Mode rmode);
 
   void movsxbq(Register dst, const Operand& src);