geary: Remove appstream-glib

As far as I can understand https://gitlab.gnome.org/GNOME/geary/-/issues/439, the dependency is only needed for `share/gettext/its/appdata.{its,loc}` files used when generating the POT file, which should not be needed at build time so https://gitlab.gnome.org/GNOME/geary/-/merge_requests/243 should never have been merged.

Additionally, `appstream-glib` is no longer maintained and `${appstream}/share/gettext/its/metainfo.{its,loc}` would be used nowadays.

Opened https://gitlab.gnome.org/GNOME/geary/-/merge_requests/856, though it is hard to test because `glib` propagates `gettext`, which also has `metainfo.its`.

Also note `appstream-glib` is still an optional build time dependency (`appstream-util validate-relax` can be used to validate the AppStream file).
But we do not care about that so it is fine that c5aa34f7ae dropped it from `nativeBuildInputs`.

pkgs/by-name/ge/geary/package.nix

@@ -39,7 +39,6 @@
   glib-networking,
   gobject-introspection,
   gspell,
-  appstream-glib,
   libstemmer,
   libytnef,
   libhandy,
@@ -70,7 +69,6 @@ stdenv.mkDerivation rec {
 
   buildInputs = [
     adwaita-icon-theme
-    appstream-glib
     enchant2
     folks
     gcr
@@ -116,6 +114,11 @@ stdenv.mkDerivation rec {
 
     patchShebangs build-aux/git_version.py
 
+    # Only used for generating .pot file
+    # https://gitlab.gnome.org/GNOME/geary/-/merge_requests/856
+    substituteInPlace meson.build \
+      --replace-fail "appstream_glib = dependency('appstream-glib', version: '>=0.7.10')" ""
+
     chmod +x desktop/geary-attach
   '';