Remove --harmony-tostring 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 205 matching lines @@
   V(harmony_object_values_entries, "harmony Object.values / Object.entries") \
   V(harmony_object_own_property_descriptors,                                 \
     "harmony Object.getOwnPropertyDescriptors()")                            \
   V(harmony_restrictive_declarations,                                        \
     "harmony limitations on sloppy mode function declarations")
 
 // Features that are shipping (turned on by default, but internal flag remains).
 #define HARMONY_SHIPPING(V)                                               \
   V(harmony_function_name, "harmony Function name inference")             \
   V(harmony_iterator_close, "harmony iterator finalization")              \
-  V(harmony_tostring, "harmony toString")                                 \
   V(harmony_regexps, "harmony regular expression extensions")             \
   V(harmony_unicode_regexps, "harmony unicode regexps")                   \
   V(harmony_sloppy, "harmony features in sloppy mode")                    \
   V(harmony_sloppy_let, "harmony let in sloppy mode")                     \
   V(harmony_sloppy_function, "harmony sloppy function block scoping")     \
   V(harmony_proxies, "harmony proxies")                                   \
   V(harmony_reflect, "harmony Reflect API")                               \
   V(harmony_regexp_subclass, "harmony regexp subclassing")                \
   V(harmony_species, "harmony Symbol.species")
 
@@ skipping 923 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