Disable the builtin checking for updates feature

When a new major update releases, the users are presented with the prompt asking them to update. It tries to download the `.deb` package, I believe (since our Flatpak uses the deb packages) and update on their system, which obviously fails, or on some Debian-based distros may do who knows what.

We should ideally disable the feature checking for new updates entirely, that is, patch it out.
Alternatively, we could change the upstream to allow disabling checking for updates through some configuration option.

Example:
https://community.anytype.io/t/anytype-linux-flatpack-doesnt-update/27542/

The issue names no repository files, tests, or entry points. Start by inspecting the Flathub packaging and the upstream update-check configuration to identify where the prompt and download behavior originate. Done means the Flatpak no longer checks for or attempts to apply updates, with the chosen packaging or upstream change verified.

Written by the indexing model from the issue text.