Bug 16636: [QA Follow-up] Move External_BakerTaylor.t to t

Bug 16636: [QA Follow-up] Move External_BakerTaylor.t to t

When we mock the preferences completely now, we do not need
db access anymore.

Test plan:
Run the test without exporting KOHA_CONF.
The test passes with some warns about koha-conf.xml.
If you point KOHA_CONF to etc/koha-conf.xml, you have no warns.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 7f4682df0dfa460c0e2ef9117e032165a45d6e79)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>