Remove outdated reference

Author: jridgewell

index.html

@@ -2256,7 +2256,7 @@ <h1><span class="secnum">2</span> Properties of the Array Prototype Object (<a h
   <emu-clause id="sec-array.prototype.groupby">
     <h1><span class="secnum">2.1</span> Array.prototype.groupBy ( <var>callbackfn</var> [ , <var>thisArg</var> ] )</h1>
     <emu-note><span class="note">Note 1</span><div class="note-contents">
-      <p><var>callbackfn</var> should be a function that accepts three arguments and returns a value that is coercible to a property. <code>groupBy</code> calls <var>callbackfn</var> once for each element in the array, in ascending order, and constructs a new object of arrays, where the property key is the return value and array is filled with the items that return that property key. <var>callbackfn</var> is called only for elements of the array which actually exist; it is not called for missing elements of the array.</p>
+      <p><var>callbackfn</var> should be a function that accepts three arguments and returns a value that is coercible to a property. <code>groupBy</code> calls <var>callbackfn</var> once for each element in the array, in ascending order, and constructs a new object of arrays, where the property key is the return value and array is filled with the items that return that property key.</p>
       <p>If a <var>thisArg</var> parameter is provided, it will be used as the <emu-val>this</emu-val> value for each invocation of <var>callbackfn</var>. If it is not provided, <emu-val>undefined</emu-val> is used instead.</p>
       <p><var>callbackfn</var> is called with three arguments: the value of the element, the index of the element, and the object being traversed.</p>
       <p><code>groupBy</code> does not directly mutate the object on which it is called but the object may be mutated by the calls to <var>callbackfn</var>.</p>

spec.emu

@@ -25,7 +25,7 @@ location: https://tc39.es/proposal-array-grouping/
   <emu-clause id="sec-array.prototype.groupby">
     <h1>Array.prototype.groupBy ( _callbackfn_ [ , _thisArg_ ] )</h1>
     <emu-note>
-      <p>_callbackfn_ should be a function that accepts three arguments and returns a value that is coercible to a property. `groupBy` calls _callbackfn_ once for each element in the array, in ascending order, and constructs a new object of arrays, where the property key is the return value and array is filled with the items that return that property key. _callbackfn_ is called only for elements of the array which actually exist; it is not called for missing elements of the array.</p>
+      <p>_callbackfn_ should be a function that accepts three arguments and returns a value that is coercible to a property. `groupBy` calls _callbackfn_ once for each element in the array, in ascending order, and constructs a new object of arrays, where the property key is the return value and array is filled with the items that return that property key.</p>
       <p>If a _thisArg_ parameter is provided, it will be used as the *this* value for each invocation of _callbackfn_. If it is not provided, *undefined* is used instead.</p>
       <p>_callbackfn_ is called with three arguments: the value of the element, the index of the element, and the object being traversed.</p>
       <p>`groupBy` does not directly mutate the object on which it is called but the object may be mutated by the calls to _callbackfn_.</p>