Consider dropping support for AGP < 4.1

[benjamin-bader]

This would let us clean up some old code, and keep our integration test suite lighter.

Actually, this may be two separate issues - we could just keep the old code around and stop providing "support", removing those versions from the integration test matrix. Not sure which option is friendlier to our users; folks stuck on those versions probably don't need to upgrade dexcount versions.

Something to ponder.