Bug 18716: Remove CGI::param warns from updatesupplier.pl

Bug 18716: Remove CGI::param warns from updatesupplier.pl

This script floods the logs with this kind of warnings.

To test:
- Run:
  $ koha-plack-err
- Edit a vendor in the acquisitions module
- Save
=> FAIL: Logs show lots of warnings that look like:
 CGI::param called in list context from package CGI::Compile::ROOT::home_vagrant_kohaclone_acqui_updatesupplier_2epl
- Apply this patch
- Run:
  $ restart_all
  $ koha-plack-err
- Edit a vendor, add/delete vendor contacts
=> SUCESS: No more warnings
- Verify editing and storing vendor contacts works as expected.
- Sign off :-D

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