Bug 29957: Replace clear_all_cookies in Auth.pm

Bug 29957: Replace clear_all_cookies in Auth.pm

Test plan:
Enable language selection and have two languages.
Change language.
Check cookie value in browser for KohaOpacLanguage.
Logout.
Verify that cookie has been cleared in browser.

Add do_not_remove_cookie line for KohaOpacLanguage in koha-conf.
Restart, flush.
Login again.
Change language.
Check cookie value in browser for KohaOpacLanguage.
Logout.
Verify that cookie still contains the language.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>