Remove old x64 code generator.

runtime/vm/vm_sources.gypi

 # Copyright (c) 2012, 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.
 
 # This file contains all sources (vm and tests) for the dart virtual machine.
 # Unit test files need to have a '_test' suffix appended to the name.
 {
   'sources': [
     'allocation.cc',
     'allocation.h',
@@ skipping 42 matching lines @@
     'class_table.h',
     'code_descriptors.cc',
     'code_descriptors.h',
     'code_descriptors_test.cc',
     'code_generator.cc',
     'code_generator.h',
     'code_generator_test.cc',
     'code_generator_arm.h',
     'code_generator_ia32.cc',
     'code_generator_ia32.h',
-    'code_generator_x64.cc',
     'code_generator_x64.h',
     'code_patcher.h',
     'code_patcher_arm.cc',
     'code_patcher_ia32.cc',
     'code_patcher_ia32_test.cc',
     'code_patcher_x64.cc',
     'code_patcher_x64_test.cc',
     'compiler.h',
     'compiler.cc',
     'compiler_stats.h',
@@ skipping 201 matching lines @@
     'virtual_memory_test.cc',
     'virtual_memory_win.cc',
     'verifier.cc',
     'verifier.h',
     'visitor.h',
     'zone.cc',
     'zone.h',
     'zone_test.cc',
   ],
 }