Editorial: Delete "the String value" in GetTemplateObject

PR #773 introduced |NotEscapeSequence|, whose TV is *undefined*.
Thus, in the List returned by TemplateStrings with _raw_ == *false*,
any element might be *undefined*.
In GetTemplateObject(), `_cookedStrings_` gets this List,
so when its elements are later extracted via `_cookedStrings_[_index_]`,
the "inline assertion" of `the String value` no longer applies.

spec.html

@@ -13156,7 +13156,7 @@ <h1>Runtime Semantics: GetTemplateObject ( _templateLiteral_ )</h1>
           1. Let _index_ be 0.
           1. Repeat, while _index_ &lt; _count_,
             1. Let _prop_ be ! ToString(_index_).
-            1. Let _cookedValue_ be the String value _cookedStrings_[_index_].
+            1. Let _cookedValue_ be _cookedStrings_[_index_].
             1. Perform ! DefinePropertyOrThrow(_template_, _prop_, PropertyDescriptor { [[Value]]: _cookedValue_, [[Writable]]: *false*, [[Enumerable]]: *true*, [[Configurable]]: *false* }).
             1. Let _rawValue_ be the String value _rawStrings_[_index_].
             1. Perform ! DefinePropertyOrThrow(_rawObj_, _prop_, PropertyDescriptor { [[Value]]: _rawValue_, [[Writable]]: *false*, [[Enumerable]]: *true*, [[Configurable]]: *false* }).