Bug 7793: redefine the field message_id as PRIMARY KEY of message_queue

Bug 7793: redefine the field message_id as PRIMARY KEY of message_queue

Making message_queue work nicely with DBIx.

DROP the existing KEY and replace with an PRIMARY KEY.
If somebody has managed to get duplicate message_ids in his/her
message_queue-table, this patch takes care of them as well, but givin
all duplicate message_id's a new id.

TEST INSTRUCTIONS: in the patch.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Amended patch: Remove change to Koha/Schema/Result/MessageQueue.pm, will
be done by the RM
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>