MXS-1891: dealloc named prepare should route to all (#174)

* dealloc named prepare route to all

* add newline

* erase from ps manager too

* little refactor

query_classifier/test/input.sql

@@ -23,3 +23,4 @@ SELECT GET_LOCK('lock1',10);
 SELECT IS_FREE_LOCK('lock1');
 SELECT IS_USED_LOCK('lock1');
 SELECT RELEASE_LOCK('lock1');
+deallocate prepare select_stmt;