Downgrading section mentions using sudo

[bilelmoussaoui]

The downgrading section mentions the needs of running the command using sudo, i don't think it's necessary

https://docs.flatpak.org/en/latest/tips-and-tricks.html#downgrading

See flatpak/flatpak#3831

[mwleeds]

Right now sudo is necessary if the thing being downgraded is in a system installation. Ideally we could use polkit as we do with other privileged operations but that would be a code change not a documentation change so it doesn't belong here.

We should update the docs to mention that sudo isn't required for a flatpak installed per-user.

[bbhtt]

We should update the docs to mention that sudo isn't required for a flatpak installed per-user.

Was solved by the above PR