[Java] Remove java/

[kou]

Describe the enhancement requested

We're moving java/ to https://github.com/apache/arrow-java .

Component(s)

Java

[lidavidm]

I am doing this in #44932. I can try to split it out.

[kou]

I think that we need GH-44829 before this. I'll do it.

[kou]

Done. Could you work on this?

[raulcd]

🥳