Use libgroove.pc from source code

Drop the `libgroove.pc` file from the libgroove package. Instead of shipping a
pkg-config config file with the package itself, use the pkg-config file provided
in the source code. This change makes it less likely that the pkg-config config
file and package itself will advertise different versions, and it makes the
pkg-config config file more likely to stay up-to-date with upstream.