[css-values-4][editorial] Fix doubled definition of <string>.

Author: tabatkins

css-values-4/Overview.bs

@@ -668,11 +668,8 @@ Textual Data Types</h2>
 	(which includes character set conversion and [[css-syntax-3#escaping|escaping]]).
 	[[!UNICODE]] [[!CSS-SYNTAX-3]]
 
-	[=Strings=], denoted by <dfn id="string-value">&lt;string></dfn>,
-	are sequences of characters representing arbitrary textual data.
-	When written literally,
-	they are delimited by double quotes or single quotes,
-	and correspond to the <<string-token>> production. [[!CSS-SYNTAX-3]].
+	[=Strings=] are quoted sequences of characters reprenting arbitrary textual data.
+	See [[#strings]] for details.
 
 	CSS <dfn export lt="CSS identifier | CSS ident | identifier | ident" for="CSS">identifiers</dfn>,
 	generically denoted by <dfn>&lt;ident></dfn>,