Remove --harmony-async-await runtime flag

src/flag-definitions.h

 // Copyright 2012 the V8 project authors. 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 defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 204 matching lines @@
 
 #ifdef V8_I18N_SUPPORT
 #define HARMONY_STAGED(V)                                          \
   HARMONY_STAGED_BASE(V)                                           \
   V(icu_case_mapping, "case mapping with ICU rather than Unibrow")
 #else
 #define HARMONY_STAGED(V) HARMONY_STAGED_BASE(V)
 #endif
 
 // Features that are shipping (turned on by default, but internal flag remains).
-#define HARMONY_SHIPPING_BASE(V) V(harmony_async_await, "harmony async-await")
+#define HARMONY_SHIPPING_BASE(V)
 
 #ifdef V8_I18N_SUPPORT
 #define HARMONY_SHIPPING(V) \
   HARMONY_SHIPPING_BASE(V)  \
   V(datetime_format_to_parts, "Intl.DateTimeFormat.formatToParts")
 #else
 #define HARMONY_SHIPPING(V) HARMONY_SHIPPING_BASE(V)
 #endif
 
 // Once a shipping feature has proved stable in the wild, it will be dropped
@@ skipping 1041 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA