Minor build improvements

Fixes for the following build issues I noticed when building hyprgraphics as a dependency:

1. usr/share/pkgconfig/* folder doesn't seem to contain anything
2. The existence of tests/test_output directory causes re-running the build to fail
3. Removed some boiler plate lines in d/copyright

There is also a lintian warning related to salsa-ci.yml.ex. But I haven't tried to fix it, since I don't fully understand how it works yet ;)