Remove dart3 compatible badge

[sigurdm]

This is no longer saying much for a package. We are at dart 3.10 at this point.

We could keep and or improve the "dart3 incompatible" badge.

@mit-mit WDYT?

[mit-mit]

Yeah, just removing it SGTM.

I don't think we're ready to exclude all the packages that don't have the badge though. There are some fairly high-use packages here:

https://pub.dev/packages?q=-is%3Adart3-compatible&sort=downloads

[isoos]

Do we want to remove the advanced search option too?

[sigurdm]

I would guess so...