[SQL] Remove ajxp_simple_store create from mq.sql

It's already in conf.sql, it was not up to date,
and postgresql before 9.x doesn't support
CREATE TABLE IF NOT EXISTS

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Merge pull request #561 from echampet/sql1

Remove ajxp_simple_store table creation from mq.sql plugin (already part of conf.sql)