Remove the barely used macro assemblers after merging their contents to the base

runtime/vm/assembler_macros_x64.h

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-// The class 'AssemblerMacros' contains assembler instruction groups that
-// are used in Dart.
-
-#ifndef VM_ASSEMBLER_MACROS_X64_H_
-#define VM_ASSEMBLER_MACROS_X64_H_
-
-#ifndef VM_ASSEMBLER_MACROS_H_
-#error Do not include assembler_macros_x64.h directly; use assembler_macros.h.
-#endif
-
-#include "vm/allocation.h"
-#include "vm/constants_x64.h"
-
-namespace dart {
-
-// Forward declarations.
-class Assembler;
-class Class;
-class Label;
-
-class AssemblerMacros : public AllStatic {
- public:
-  // Inlined allocation of an instance of class 'cls', code has no runtime
-  // calls. Jump to 'failure' if the instance cannot be allocated here.
-  // Allocated instance is returned in 'instance_reg'.
-  // Only the tags field of the object is initialized.
-  static void TryAllocate(Assembler* assembler,
-                          const Class& cls,
-                          Label* failure,
-                          bool near_jump,
-                          Register instance_reg);
-
-  // Set up a dart frame on entry with a frame pointer and PC information to
-  // enable easy access to the RawInstruction object of code corresponding
-  // to this frame.
-  // The dart frame layout is as follows:
-  //   ....
-  //   ret PC
-  //   saved RBP     <=== RBP
-  //   pc (used to derive the RawInstruction Object of the dart code)
-  //   locals space  <=== RSP
-  //   .....
-  // This code sets this up with the sequence:
-  //   pushq rbp
-  //   movq rbp, rsp
-  //   call L
-  //   L: <code to adjust saved pc if there is any intrinsification code>
-  //   .....
-  static void EnterDartFrame(Assembler* assembler, intptr_t frame_size);
-
-  // Set up a stub frame so that the stack traversal code can easily identify
-  // a stub frame.
-  // The stub frame layout is as follows:
-  //   ....
-  //   ret PC
-  //   saved RBP
-  //   pc (used to derive the RawInstruction Object of the stub)
-  //   .....
-  // This code sets this up with the sequence:
-  //   pushq rbp
-  //   movq rbp, rsp
-  //   pushq immediate(0)
-  //   .....
-  static void EnterStubFrame(Assembler* assembler);
-
-  // Instruction pattern from entrypoint is used in dart frame prologs
-  // to set up the frame and save a PC which can be used to figure out the
-  // RawInstruction object corresponding to the code running in the frame.
-  // entrypoint:
-  //   pushq rbp          (size is 1 byte)
-  //   movq rbp, rsp      (size is 3 bytes)
-  //   call L             (size is 5 bytes)
-  //   L:
-  static const intptr_t kOffsetOfSavedPCfromEntrypoint = 9;
-};
-
-}  // namespace dart.
-
-#endif  // VM_ASSEMBLER_MACROS_X64_H_