Bug 21865: improve remove_unused_authorities.pl script

Bug 21865: improve remove_unused_authorities.pl script

remove_unused_authorities.pl script can be improved.

This patch changes changes verbosity so than test mode can be used
to know the autorities that are used and those that can be deleted.
It also writes a line in output if limited authority type(s).

This patch also removes the unused vars $thresholdmin and $thresholdmax.

It also changes the query to use SQL with parameters for authority types.

Test plan :
1) On a catalog create a new authority
2) Be sure catalog is well indexed
3) Run misc/migration_tools/remove_unused_authorities.pl -t
4) You will see the line :
   *** Testing only, authorities will not be deleted. ***
5) You will see lines of :
   authid=x type=y : used X time(s)
6) You will see the line for the authority created in 1) :
   authid=x type=y : can be deleted
7) You will see at the end :
   x authorities parsed
   y can be deleted because unused
   z unchanged because used
8) Run misc/migration_tools/remove_unused_authorities.pl
9) You don't see the line :
   *** Testing only, authorities will not be deleted. ***
10) You will see lines of :
   authid=x type=y : used X time(s)
11) You will see the line for the authority created in 1) :
   authid=x type=y : deleted
12) You will see at the end :
   x authorities parsed
   y deleted because unused
   z unchanged because used
13) Run misc/migration_tools/remove_unused_authorities.pl --auth NP --auth CO
14) You see the line :
    Restricted to authority type(s) : NP,CO.

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>