Build: remove .java-version file

[szehon-ho]

This was added in #3651, and I would like to propose its removal. We no longer have Spark 2, which was the only reason Java 8 was set here.

This is actually now the wrong default for jenv users.

[szehon-ho]

@findepi @nastra @RussellSpitzer does it make sense?

[nastra]

I'm ok removing this because I don't use it, but let's see what @findepi thinks

[findepi]

.java-version is used by jenv to pick the right version for particular project. I don't know any other convention or tooling that would solve this mundane problem of choosing the right JDK, which might be a challenge for people who work on different projects having different minimum JDK versions. I do recommend having such a file (with correct contents of course), but it's up to project maintainers to decide. After all the maintainers choose whether they maintain or drop a

[szehon-ho]

In my thought, as build.gradle supports building of all Java versions, it could be a surprise to jenv users that Iceberg overrides the user's global default. Also i took a brief look at some other projects like Parquet/Spark/Flink/Hive, and didn't see .java-version there. I think this made sense before when Spark 2 was not built without java8, but now that has been removed and don't see a strong reason to default Iceberg to a specific java version overriding the user's default. That being said, I can leave this a little bit and see if anyone has strong comments against its removal.

[aokolnychyi]

Are there any other modules that are only compiled using JDK 8? Hive? Is that even being used?

I guess the primary benefit of having this file was to force building of all modules, which is helpful to catch compile-time errors after changes in core. Given that we changed our deprecation model and added support for quite a bit of Java versions at this point, I see how it may be surprising to have this override. I am OK either way but we need to double check our release scripts to make sure they have proper validation. We still have to use Java 8 there.

[szehon-ho]

I think this file is for jenv users only. There is a explicit check for java version in release: https://github.com/apache/iceberg/blob/master/deploy.gradle#L21 so we should be fine there as I can see.

[dramaticlly]

LGTM, I use jenv for building iceberg locally and I dont think we need to dictate on java version here

[szehon-ho]

Merging, I think there's no strong objection. If we have some reason in future to must build with a certain Java version, we can put this back. For now, as Iceberg can be built in many distro using different Java version, this allows more flexibility. Thanks everyone for discussions.