rpm: Exclude vendored libraries from the list of provides

The RPM automatic dependency generator adds provides for all
libraries under %{_libdir}. When vendoring libraries you must disable
this behaviour, otherwise other packages that link against Qt will
not pull in the distro qt packages if jami-libqt is already installed

Change-Id: I3f0a018ea12be7f29d04ca4441cbfdebc2efb909