meson: Fix unknown kw argument in gnome.generate_gir
This argument has been removed in Meson 0.61.0:
gcr-gtk4/meson.build:87:2: 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.
This was fixed for gcr-gtk3/meson.build (at that point ui/meson.build) in commit b3ca1d02 ("meson: Fix unknown kw argument in gnome.generate_gir")