Makefile: don't install gir files
Makefile: don't install gir files

Doesn't make sense for private libs, they will still be built and
available in the repo when building and testing knowledge lib,
but because nothing else will use knowledge lib, there's no need
to distribute them all.
[endlessm/eos-sdk#3108]

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib