Remove mention of `RegExp.$input`

src/regexp.js

 // 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 relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Array = global.Array;
 
 var $RegExp = global.RegExp;
@@ skipping 376 matching lines @@
   InstallFunctions($RegExp.prototype, DONT_ENUM, $Array(
     "exec", RegExpExec,
     "test", RegExpTest,
     "toString", RegExpToString,
     "compile", RegExpCompileJS
   ));
 
   // The length of compile is 1 in SpiderMonkey.
   %FunctionSetLength($RegExp.prototype.compile, 1);
 
-  // The properties input, $input, and $_ are aliases for each other.  When this
+  // The properties `input` and `$_` are aliases for each other.  When this
   // value is set the value it is set to is coerced to a string.
   // Getter and setter for the input.
   var RegExpGetInput = function() {
     var regExpInput = LAST_INPUT(lastMatchInfo);
     return IS_UNDEFINED(regExpInput) ? "" : regExpInput;
   };
   var RegExpSetInput = function(string) {
     LAST_INPUT(lastMatchInfo) = ToString(string);
   };
 
@@ skipping 47 matching lines @@
 
   for (var i = 1; i < 10; ++i) {
     %DefineAccessorPropertyUnchecked($RegExp, '$' + i,
                                      RegExpMakeCaptureGetter(i), NoOpSetter,
                                      DONT_DELETE);
   }
   %ToFastProperties($RegExp);
 }
 
 SetUpRegExp();