[promises] Clean up promise utils and remove dead code

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 1614 matching lines @@
     "src/profiler/sampling-heap-profiler.cc",
     "src/profiler/sampling-heap-profiler.h",
     "src/profiler/strings-storage.cc",
     "src/profiler/strings-storage.h",
     "src/profiler/tick-sample.cc",
     "src/profiler/tick-sample.h",
     "src/profiler/tracing-cpu-profiler.cc",
     "src/profiler/tracing-cpu-profiler.h",
     "src/profiler/unbound-queue-inl.h",
     "src/profiler/unbound-queue.h",
-    "src/promise-utils.cc",
-    "src/promise-utils.h",
     "src/property-descriptor.cc",
     "src/property-descriptor.h",
     "src/property-details.h",
     "src/property.cc",
     "src/property.h",
     "src/prototype.h",
     "src/regexp/bytecodes-irregexp.h",
     "src/regexp/interpreter-irregexp.cc",
     "src/regexp/interpreter-irregexp.h",
     "src/regexp/jsregexp-inl.h",
@@ skipping 1412 matching lines @@
   ]
 
   configs = [
     ":external_config",
     ":internal_config_base",
   ]
 }
 
 v8_fuzzer("wasm_data_section_fuzzer") {
 }