Editorial: Remove unnecessary undefined type from property descriptor tests

`Is{Accessor,Data,Generic}Descriptor` are never called with `undefined`.

Author: anba

spec.html

@@ -4411,13 +4411,12 @@ <h1>The Property Descriptor Specification Type</h1>
       <emu-clause id="sec-isaccessordescriptor" type="abstract operation">
         <h1>
           IsAccessorDescriptor (
-            _Desc_: a Property Descriptor or *undefined*,
+            _Desc_: a Property Descriptor,
           ): a Boolean
         </h1>
         <dl class="header">
         </dl>
         <emu-alg>
-          1. If _Desc_ is *undefined*, return *false*.
           1. If _Desc_ has a [[Get]] field, return *true*.
           1. If _Desc_ has a [[Set]] field, return *true*.
           1. Return *false*.
@@ -4427,13 +4426,12 @@ <h1>
       <emu-clause id="sec-isdatadescriptor" type="abstract operation">
         <h1>
           IsDataDescriptor (
-            _Desc_: a Property Descriptor or *undefined*,
+            _Desc_: a Property Descriptor,
           ): a Boolean
         </h1>
         <dl class="header">
         </dl>
         <emu-alg>
-          1. If _Desc_ is *undefined*, return *false*.
           1. If _Desc_ has a [[Value]] field, return *true*.
           1. If _Desc_ has a [[Writable]] field, return *true*.
           1. Return *false*.
@@ -4443,13 +4441,12 @@ <h1>
       <emu-clause id="sec-isgenericdescriptor" type="abstract operation">
         <h1>
           IsGenericDescriptor (
-            _Desc_: a Property Descriptor or *undefined*,
+            _Desc_: a Property Descriptor,
           ): a Boolean
         </h1>
         <dl class="header">
         </dl>
         <emu-alg>
-          1. If _Desc_ is *undefined*, return *false*.
           1. If IsAccessorDescriptor(_Desc_) is *true*, return *false*.
           1. If IsDataDescriptor(_Desc_) is *true*, return *false*.
           1. Return *true*.
@@ -14079,6 +14076,7 @@ <h1>
             1. Return ? ArraySetLength(_A_, _Desc_).
           1. Else if _P_ is an array index, then
             1. Let _lengthDesc_ be OrdinaryGetOwnProperty(_A_, *"length"*).
+            1. Assert: _lengthDesc_ is not *undefined*.
             1. Assert: IsDataDescriptor(_lengthDesc_) is *true*.
             1. Assert: _lengthDesc_.[[Configurable]] is *false*.
             1. Let _length_ be _lengthDesc_.[[Value]].
@@ -14168,6 +14166,7 @@ <h1>
           1. If SameValueZero(_newLen_, _numberLen_) is *false*, throw a *RangeError* exception.
           1. Set _newLenDesc_.[[Value]] to _newLen_.
           1. Let _oldLenDesc_ be OrdinaryGetOwnProperty(_A_, *"length"*).
+          1. Assert: _oldLenDesc_ is not *undefined*.
           1. Assert: IsDataDescriptor(_oldLenDesc_) is *true*.
           1. Assert: _oldLenDesc_.[[Configurable]] is *false*.
           1. Let _oldLen_ be _oldLenDesc_.[[Value]].