fix primary key syntax

Author: dnauck

core/src/plugins/mq.sql/create.pgsql

@@ -1,5 +1,5 @@
 CREATE TABLE IF NOT EXISTS ajxp_mq_queues (
   channel_name varchar(255) NOT NULL,
   content bytea NOT NULL,
-  constraint pk primary key(channel_name)
+  primary key(channel_name)
 );