[promises] Clean up promise utils and remove dead code

src/v8.gyp

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 1123 matching lines @@
         'profiler/sampling-heap-profiler.cc',
         'profiler/sampling-heap-profiler.h',
         'profiler/strings-storage.cc',
         'profiler/strings-storage.h',
         'profiler/tick-sample.cc',
         'profiler/tick-sample.h',
         'profiler/tracing-cpu-profiler.cc',
         'profiler/tracing-cpu-profiler.h',
         'profiler/unbound-queue-inl.h',
         'profiler/unbound-queue.h',
-        'promise-utils.h',
-        'promise-utils.cc',
         'property-descriptor.cc',
         'property-descriptor.h',
         'property-details.h',
         'property.cc',
         'property.h',
         'prototype.h',
         'regexp/bytecodes-irregexp.h',
         'regexp/interpreter-irregexp.cc',
         'regexp/interpreter-irregexp.h',
         'regexp/jsregexp-inl.h',
@@ skipping 1341 matching lines @@
       'conditions': [
         ['want_separate_host_toolset_mkpeephole==1', {
           'toolsets': ['host'],
         }, {
           'toolsets': ['target'],
         }],
       ],
     },
   ],
 }