Editorial: Simplify RegExpInitialize (tc39#2391)

After the merge of tc39#2531, `_patternCharacters_` is no longer
used/referenced, so remove the steps that define it.

Also, add a NOTE after step 13.

spec.html

@@ -35820,15 +35820,14 @@ <h1>
             1. If _F_ contains *"u"*, let _u_ be *true*; else let _u_ be *false*.
             1. If _u_ is *true*, then
               1. Let _patternText_ be ! StringToCodePoints(_P_).
-              1. Let _patternCharacters_ be a List whose elements are the code points of _patternText_.
             1. Else,
               1. Let _patternText_ be the result of interpreting each of _P_'s 16-bit elements as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
-              1. Let _patternCharacters_ be a List whose elements are the code unit elements of _P_.
             1. Let _parseResult_ be ParsePattern(_patternText_, _u_).
             1. If _parseResult_ is a non-empty List of *SyntaxError* objects, throw a *SyntaxError* exception.
             1. Assert: _parseResult_ is a |Pattern| Parse Node.
             1. Set _obj_.[[OriginalSource]] to _P_.
             1. Set _obj_.[[OriginalFlags]] to _F_.
+            1. NOTE: The definitions of _DotAll_, _IgnoreCase_, _Multiline_, and _Unicode_ in <emu-xref href="#sec-notation"></emu-xref> refer to this value of _obj_.[[OriginalFlags]].
             1. Set _obj_.[[RegExpMatcher]] to CompilePattern of _parseResult_.
             1. Perform ? Set(_obj_, *"lastIndex"*, *+0*<sub>𝔽</sub>, *true*).
             1. Return _obj_.