extensions-app: Stop setting VERSION in config

We set it because it was referenced by (here unused) code
in ExtensionUtils. This changed in commit 4a0b0e26c7, so
stop setting it.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2844>

subprojects/extensions-app/js/misc/config.js.in

@@ -1,2 +1 @@
-var PACKAGE_VERSION = '@PACKAGE_VERSION@';
 var PROFILE = '@PROFILE@';

subprojects/extensions-app/js/misc/meson.build

@@ -2,7 +2,6 @@ config_js = configure_file(
   input: 'config.js.in',
   output: '@BASENAME@',
   configuration: {
-    'GETTEXT_VERSION': meson.project_version(),
     'PROFILE': get_option('profile'),
   }
 )