CPP: delete the deprecated `AnalysedString` class

cpp/ql/lib/semmle/code/cpp/commons/StringAnalysis.qll

@@ -27,9 +27,6 @@ predicate canValueFlow(Expr fromExpr, Expr toExpr) {
   fromExpr = toExpr.(ConditionalExpr).getElse()
 }
 
-/** DEPRECATED: Alias for AnalyzedString */
-deprecated class AnalysedString = AnalyzedString;
-
 /**
  * An analyzed null terminated string.
  */