remove superfluous note

Author: gregsdennis

jsonschema-core.md

@@ -341,9 +341,7 @@ Plain name fragments MUST follow XML's [`NCName` production](#xml-names), which
 allows for compatibility with the recommended plain name
 [syntax](#w3crec-xptr-framework-20030325) for XML-based media types.  For
 convenience, the `NCName` syntax is reproduced here in ABNF form, using
-a minimal set of rules: [^20]
-
-[^20] Note that the previous syntax for plain name fragment is a subset of this syntax, which used only the first line of each of the `NCNameStartChar` and `NCNameChar` rules.
+a minimal set of rules:
 
 ```abnf
 NCName          = NCNameStartChar *NCNameChar