flatpak: simplify the manifest

build-aux/org.gnome.TourDevel.json

 {
     "app-id" : "org.gnome.TourDevel",
     "runtime" : "org.gnome.Platform",
-    "runtime-version" : "3.36",
+    "runtime-version" : "master",
     "sdk" : "org.gnome.Sdk",
     "sdk-extensions" : [
         "org.freedesktop.Sdk.Extension.rust-stable"
@@ -29,29 +29,6 @@
     },
     "modules" : [
         {
-            "name" : "libhandy",
-            "buildsystem" : "meson",
-            "config-opts" : [
-                "-Dintrospection=disabled",
-                "-Dgtk_doc=false",
-                "-Dtests=false",
-                "-Dexamples=false",
-                "-Dvapi=false",
-                "-Dglade_catalog=disabled"
-            ],
-            "cleanup" : [
-                "/include",
-                "/lib/pkgconfig"
-            ],
-            "sources" : [
-                {
-                    "type" : "git",
-                    "url" : "https://gitlab.gnome.org/GNOME/libhandy.git",
-                    "commit" : "94313c206258860b2428712e7ece1d02c5177857"
-                }
-            ]
-        },
-        {
             "name" : "gnome-tour",
             "buildsystem" : "meson",
             "config-opts" : [