[regexp] remove no-op RegExp.multiline accessor and alias

test/mozilla/mozilla.status

 # Copyright 2011 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 72 matching lines @@
 
   # Date.prototype is an Object, not a Date
   'ecma/Date/15.9.5': [FAIL],
 
   # In ES6, the completion value of a 0-iterations loop is 'undefined'.
   'ecma/Statements/12.6.3-2': [PASS, FAIL],
 
   # ES2015 ToLength semantics
   'ecma_3/RegExp/15.10.6.2-2': [FAIL],
 
+  # RegExp.multiline is not part of any ECMAScript specification, and is
+  # slated for deprecation in Mozilla
+  # (https://bugzilla.mozilla.org/show_bug.cgi?id=1220457)
+  'js1_5/Regress/regress-418504': [FAIL],
+
   ##################### SKIPPED TESTS #####################
 
   # This test checks that we behave properly in an out-of-memory
   # situation.  The test fails in V8 with an exception and takes a long
   # time to do so.
   'js1_5/Regress/regress-271716-n': [SKIP],
 
   # BUG(960): This test has an insane amount of output when it times out,
   # messing up ability to see other failures on the waterfall.
   'js1_5/extensions/regress-342960': [SKIP],
@@ skipping 860 matching lines @@
   'ecma_3/RegExp/regress-307456': [SKIP],
   'js1_5/Regress/regress-303213': [SKIP],
   'js1_5/extensions/regress-330569': [SKIP],
   'js1_5/extensions/regress-351448': [SKIP],
   'js1_5/extensions/regress-336410-1': [SKIP],
 
   #BUG(3152): Avoid C stack overflow.
   'js1_5/extensions/regress-355497': [FAIL_OK, 'Flags: --sim-stack-size=512'],
 }],  # 'arch == arm64 and simulator_run == True'
 ]