Revert "meson: Add schemasdir and giomoduledir to gio dependency"

This reverts commit 5aa03882ca.

It fails to compile on newer Meson versions with
`--fatal-meson-warnings` due to:
```
WARNING: Project targeting '>= 0.52.0' but tried to use feature introduced in '0.54.0': variables arg in declare_dependency.
gio/meson.build:833:0: ERROR: Fatal warnings enabled, aborting
```

That happens regardless of the fact that we’ve correctly limited the use
of the `variables` argument to only when building with Meson ≥ 0.56.
Unfortunately Meson can’t statically detect that the argument is
conditional.

Bumping GLib’s Meson dependency is too much work right now, so this MR
unfortunately has to be reverted.

gio/meson.build

@@ -819,22 +819,9 @@ endif
 
 schemas_subdir = join_paths('glib-2.0', 'schemas')
 
-# Work around variables kwarg requiring Meson 0.56
-declare_dependency_kwargs = {}
-if meson.version().version_compare('>=0.56.0')
-  declare_dependency_kwargs = {
-    'variables': [
-      'schemasdir=' + join_paths(glib_datadir, schemas_subdir),
-      'giomoduledir=' + glib_giomodulesdir,
-    ]
-  }
-endif
-
 libgio_dep = declare_dependency(link_with : libgio,
   dependencies : [libgmodule_dep, libgobject_dep, gioenumtypes_dep],
-  include_directories : [gioinc],
-  kwargs : declare_dependency_kwargs,
-)
+  include_directories : [gioinc])
 
 pkg.generate(libgio,
   requires : ['glib-2.0', 'gobject-2.0'],