[Debian GNUstep maintainers] Restoring /usr/bin/pl

[Yavor Doganov]

In gnustep-base/1.13.0-7 (back in December 2006) we renamed the pl
utility to /usr/bin/plio due to a conflict with /usr/bin/pl from
src:tendra.  However, the tendra package was removed from Debian in
2016.  AFAICS there are no current file conflicts so unless someone
objects I suggest to restore /usr/bin/pl in 1.28.0-1.

Rationale: We should attempt to be as close to upstream as possible;
this minimizes the Debian-specific changes and avoids user surprises.
It would also enable us to remove the build-dep on dh-exec.