Bug 16444: Make C4::Tags plack safe

Bug 16444: Make C4::Tags plack safe

C4::Tags use a package variable to cache the pref
TagsExternalDictionary, it's not needed and not safe.

There is not test plan, just make sure the changes are consistent.

Signed-off-by: Srdjan <srdjan@catalyst.net.nz>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit fff754a7fc7a99dad6a35129b8a7dd170684f2bf)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
(cherry picked from commit 97a3f03970e1aa8d3eba5e5502f092202e43349b)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>