Bug 17097: Fix CSRF in deletemem.pl

Bug 17097: Fix CSRF in deletemem.pl

If an attacker can get an authenticated Koha user to visit their page
with the url below, they can delete patrons details.

  /members/deletemem.pl?member=42

Test plan:

0/ Do not apply any patches
1/ Adapt and hit the url above
=> The patron will be deleted without confirmation
2/ Apply first patch
3/ Hit the url
=> you will get a confirmation page
4/ Hit /members/deletemem.pl?member=42&delete_confirmed=1
=> The patron will be deleted without confirmation
5/ Apply the second patch (this one)
6/ Hit /members/deletemem.pl?member=42&delete_confirmed=1
=> you will get a crash "Wrong CSRF token" (no need to stylish)
7/ Delete a patron from the detail page and confirm the deletion
=> you will be redirected to the patron module home page and the patron
has been deleted

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>