Duplicate assets when filtering by multiple groups or location

I found the exact commit that added the "Group" filter option to the Animal's list: https://github.com/farmOS/farmOS/commit/e7e808de70c9ca2607bac74a7735d5f7...

Notably, it allowed "multiple" selections right from the start. What this tells me is that we did NOT add the ability to select multiple groups as a separate intentional feature request. I just enabled multiple selections by default, not knowing that it would have this duplicate issue.

So, to me this means that when I added that filter, I also introduced this bug, simply by allowing multiple selections.

This means that technically, we have potentially two separate things:

1. A bug: selecting multiple causes duplicates
2. A feature request: the ability to select multiple (without causing duplicates)

So, we could start by fixing #1, by disabling the ability to select multiple. It would still be possible to filter by group, but users would be restricted to a single selection at a time.

Then, if desired, we could open another feature request that adds the ability to select multiple back, but dig into it deeper and see if there's a way to do it without causing duplicates. It's possible that this will end up requiring custom Views handler code, which could be complicated. So we should also weigh the cost/benefit.

I fixed this bug by eliminating the option to filter by multiple groups or locations.

If we want to restore that ability, we will need to start a new feature request: "Ability to filter by multiple groups/locations (without causing duplicates)"