Drop no-pie-on-ubuntu tweak in postgis?

[Christoph Berg]

Re: Bas Couwenberg 2019-07-16 <0e3b15750b80b7ae9eb0826a7629e585 at xs4all.nl>
> > We have decent test coverage now, can we drop this bit in postgis?
> 
> We might be able to drop the PIE handling on Ubuntu, but we're not testing
> on those Ubuntu environment AFAIK.

I forgot to mention that I'm testing+building postgis on
xenial+bionic+disco. (disco is already not in the that list.)

> If you can confirm that pie now works on xenial & bionic we can drop this
> code (and the lsb_release B-D).

I don't see any issues besides the general i386 one tracked in
https://trac.osgeo.org/postgis/ticket/4407

I'll do some clean up of the rule files; currently I'm working on
making the pg-postgis-3 package actually depend on
pg-postgis-3-scripts as getting that installed without the dependency
is really painful, and bad UX. I hope that using "alternatives" for
the *.control files does the trick. Will push a branch for review.

Christoph