ruby: remove unused predicate from NfaUtilsSpecific

Author: erik-krogh

ruby/ql/lib/codeql/ruby/security/regexp/NfaUtilsSpecific.qll

@@ -63,14 +63,6 @@ module RegExpFlags {
     root.getLiteral().isIgnoreCase()
   }
 
-  /**
-   * Gets the flags for `root`, or the empty string if `root` has no flags.
-   */
-  string getFlags(RegExpTerm root) {
-    root.isRootTerm() and
-    result = root.getLiteral().getFlags()
-  }
-
   /**
    * Holds if `root` has the `s` flag for multi-line matching.
    */