When someone uses our pc file they shouldn't need to explicitly add gobject to compile

Testing Done:
Ran configure and verified that `${builddir}/meson-private/gnt.pc` properly had `gobject-2.0` in `Required`

```
Requires: glib-2.0 >= 2.16.0, gobject-2.0
```

Reviewed at https://reviews.imfreedom.org/r/1478/