Build: copr: Fix the copr Makefile.

• According to the docs, the spec file variable can just be ignored if it's not needed. So get rid of that.

• Remove the dnf command. For running locally, this will require being root which means a bunch of build artifacts will be created with root permissions. That's kind of a mess. Additionally, we can specify which packages need to be installed from inside the copr web UI so there's no need to do it here.

Ref T912