Disable f-e-d-c

Flathubbot has been creating too much PR without any success.

I think it would be good to close automatic PR creation until the data-checker optimizations are complete.

See: https://github.com/flathub/com.devolutions.remotedesktopmanager/pulls?q=is%3Apr+author%3Aflathubbot+

Author: yakushabb

flathub.json

@@ -1,3 +1,4 @@
 {
+  "disable-external-data-checker": true,
   "only-arches": ["x86_64", "aarch64"]
 }