on the highscores/top5 screen, only show the highest score per player

[barbeque-squared]

…. and also adds a TODO because the filter is useless now? (not that it did anything to begin with...)
I'm not interest in seeing how often a certain player has set a good score, I'm interested in seeing how it compares to other players. I've been using this since August 2022 and is really nice.

what this PR does in pictures:
before:

after:

[barbeque-squared]

As commented by servok in Discord:

In USDX 2020.4.0, we use the "1 Highscore per Player"-option for years now, and it's very good. You still see if you were better than your highscore. There is an option under options-advanced saying "Höchstpunktzahlen: Spieler" or "Höchstpunktzahlen: Alle", switching between the alternatives

The score code even does something with this option, but it's not very intuitive. Until I was pointed to it, I wasn't even aware of this option. Yeah this PR is invalid, I'll change to to WIP for now and close it once I have a PR that refactors this whole bit of code, as well as how the setting is stored (it's currently a number and apparently "1" is the Player option -- this should really be an enum)

Still leaves the debate of what should be the default (imo "Player") but we'll get to that once this mess is gone.