meson: Fix unknown kw argument in gnome.generate_gir

This argument has been removed in Meson 0.61.0:

gck/meson.build:130:2: ERROR: gnome.generate_gir got unknown keyword arguments "packages"

https://github.com/mesonbuild/meson/commit/f8fc5cb860465718fe7c79a1bf1fe00659f138de:

The packages argument to gnome.generate_gir was allowed, but never did anything, so stop passing it.

Fixes #89 (closed)

(Backport of !81 (merged))