Bug 26337: Pass skip_merge to DelAuthority when removing unsused authorities

Bug 26337: Pass skip_merge to DelAuthority when removing unsused authorities

This script checks that an authority is not being used before deleting it.
We do not need to check biblios for the authority id as we have already verified it is unused.

TO test:
 1 - Reset db to koha test database
 2 - perl misc/migration_tools/remove_unused_authorities.pl -t
 3 - Note a number of unsued authorities
 4 - perl misc/migration_tools/remove_unused_authorities.pl -c
 5 - Note authorities are removed
 6 - Reset db
 7 - Apply patch
 8 - perl misc/migration_tools/remove_unused_authorities.pl -t
 9 - Note results are the same
10 - perl misc/migration_tools/remove_unused_authorities.pl -c
11 - Note results are the same

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>