purism-librem5: replace gpsd with gnss-share

gnss-share is a location provider I wrote for the librem 5's GPS module, and can be used directly from geoclue. It allows saving and loading A-GPS data (manual steps, for now) to facilitate faster fixes.

I'm not completely happy with having to use sed to patch geoclue's conf, but:

1. I really only need to change 1 line

2. there's a non-zero chance geoclue's conf will be changed in aports if new permissions are required for things later

So carrying the config in the device package and using "replaces=geoclue" (like the postmarketos-* stuff) didn't seem like a maintainable solution long term since the geoclue conf might gain needed fixes/features that might make a copy in the device package outdated...