Bug 25889: Increase performance of debian/list-deps script

Bug 25889: Increase performance of debian/list-deps script

to test... (on a i7-2600 vm with 8 cores)

1/ run script, note execution time
    $ time ./debian/update-control
    real    8m5.000s

2/ copy old file
    $ cp ./debian/control control.old

3/ apply patch

4/ run updated script, note execution time is smaller
    $ time ./debian/update-control
    real    2m14.000s

5/ copy new file
    $ cp ./debian/control control.new

6/ confirm old and new control files are identical
    $ diff control.old control.new | wc -l
    0

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>