Bug 17913: We always need some housekeeping

Bug 17913: We always need some housekeeping

Remove some commented warnings
Remove the commented old code at the end of sub merge
Explicitly set merge mode in the first subtest
Move the return to loose mode from the second subtest to the third

Test plan:
Run t/db_dependent/Authorities/Merge.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>