Bug 20201: Silence warnings triggered by admin/aqplan.pl

Bug 20201: Silence warnings triggered by admin/aqplan.pl

TEST PLAN
---------
0) back up DB
1) Run the following commands on a kohadevbox:
    reset_all
    git bz apply 20185
    echo | sudo tee /var/log/koha/kohadev/plack-error.log
    restart_all
2) Navigate in a staff client:
    Home -> Administration -> Budgets -> Edit -> Planning by libraries
   -- could be any of the planning, but by libraries is nicely visible
   on screen.
3) Run the following commands:
    cat /var/log/koha/kohadev/plack-error.log
   -- several warnings.
4) Run the following commands:
    git bz apply 20201
    echo | sudo tee /var/log/koha/kohadev/plack-error.log
    restart_all
5) repeat step 2 and refresh the staff client page.
   -- this time warnings related to aqplan.pl are not there.
6) run koha qa test tools

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>