CAS-1076 mark as final ticketId parameter to deleteTicket

Marks ticketId parameter to deleteTicket() as final since ticketId
assignment is not and is not expected to be modified in deleteTicket()
implementation.

cas-server-integration-ehcache/src/main/java/org/jasig/cas/ticket/registry/EhCacheTicketRegistry.java

@@ -52,7 +52,7 @@ public void addTicket(final Ticket ticket) {
         }
     }
 
-    public boolean deleteTicket(String ticketId) {
+    public boolean deleteTicket(final String ticketId) {
         if (ticketId == null) {
             return false;
         }