l10n: Eliminated STRING_TASK_VALID_RECUR

src/recur2.cpp

@@ -253,7 +253,7 @@ static Datetime generateNextDueDate (
   std::string::size_type idx = 0;
   Duration p;
   if (! p.parse (period, idx))
-    throw std::string (format (STRING_TASK_VALID_RECUR, period));
+    throw std::string (format ("The recurrence value '{1}' is not valid.", period));
 
   return current + p.toTime_t ();
 */