Bug 13437: Perltidy some plugin files before conversion

Bug 13437: Perltidy some plugin files before conversion

Preliminary work before converting to new plugin style. Several files still
contained tabs or had strange indentation.

Perltidied: marc21_linking_section.pl
Perltidied: marc21_field_007.pl
Perltidied: marc21_leader_authorities.pl
Perltidied: marc21_leader.pl
Perltidied: marc21_leader_book.pl
Perltidied: marc21_leader_computerfile.pl
Perltidied: marc21_leader_video.pl

Test plan:
Run perltidy -pro=xt/perltidyrc on marc21_linking_section and compare.
Try another one too :)

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Minor differences on comparison :)
No errors

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>