Remove more dead code after Object.observe removal

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 63 matching lines @@
   # Function length properties are configurable in ES6
   'ecma/Array/15.4.4.3-1': [FAIL],
   'ecma/Array/15.4.4.4-1': [FAIL],
   'ecma/Array/15.4.4.4-2': [FAIL],
   'ecma/String/15.5.4.10-1': [FAIL],
   'ecma/String/15.5.4.11-1': [FAIL],
   'ecma/String/15.5.4.7-2': [FAIL],
   'ecma/String/15.5.4.8-1': [FAIL],
   'ecma/String/15.5.4.9-1': [FAIL],
 
+  # __defineGetter__ is spec'ed in ES2016+ to respect readonly properties
+  # and throw. These tests fail in modern Firefox (tested: 38.7.1) too.
+  'js1_5/extensions/regress-313500': [FAIL],
+  'js1_5/extensions/regress-325269': [FAIL],
+
   # 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],
 
   # Escaped keywords are early errors in ES6
@@ skipping 876 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'
 ]