Remove experimental maven download feature.

[mbien]

got replaced by mvnw #3198 / #7076 (comment)

[mbien]

since gradle support is going to be 17+, maybe we should do this here too. I saw some sig validation issues in the log when I tried this so I didn't really bother. However that was before #7117, maybe I should give it another try.

[matthiasblaesing]

The change makes sense to me, I left a minor suggestion inline. I hope that maven does not go down the "lets create a product that breaks on every minor JDK change" (aka gradle) route, but that is a different discussion.

[mbien]

I hope that maven does not go down the "lets create a product that breaks on every minor JDK change" (aka gradle) route, but that is a different discussion.

I am following the maven dev list a bit and I don't think we have to worry about that. Maven 4 won't have a different approach to compatibility than Maven 3 has. Maven 3 will also stick around for a while in maintenance mode.