[MINOR][CORE] Remove unused variables, unused imports, etc.

[imback82]

What changes were proposed in this pull request?

• Remove unused variables.
• Remove unused imports.
• Change var to val in few places.

How was this patch tested?

Unit tests.

[dongjoon-hyun]

Thank you for your first contribution and welcome, @imback82 . I have a few comments.

• We use [MINOR] tag if we don't have SPARK JIRAs.
• Could you find more instances in core module? We usually recommend to do this kind of tasks module by module.

[imback82]

• We use [MINOR] tag if we don't have SPARK JIRAs.

Thanks. I will follow this from the next PR.

• Could you find more instances in core module? We usually recommend to do this kind of tasks module by module.

I compiled with -Xlint:unused for the core module. I fixed most of the warnings for unused local variable and unused imports (there were some false positives since scaladoc was referring to the imports). I didn't fix unused private variable, private method, and private default arguments; there are about 50 of them and I can fix them in a separate PR if needed.

[dongjoon-hyun]

Ur, thank you for the update, but let's remove unused imports stuff. You can get reviews later in another PR. It's good to have but sometime it's on the edge due to the intrusiveness. Also, it's beyond the scope of PR title.

[dongjoon-hyun]

@imback82 . Please see the comments. This PR removes live codes.

[srowen]

Except for keeping the private setActive method, I think this is fine as a general cleanup of dead code and imports

[dongjoon-hyun]

ok to test

[dongjoon-hyun]

I'll leave this PR to you, @srowen ~ Thank you, @srowen and @imback82 .

[SparkQA]

Test build #106479 has finished for PR 24857 at commit f55f684.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[imback82]

@srowen any update on this?

@HyukjinKwon I just noticed that you referenced this PR from #24858. Do you have the same concern with this PR? If messing with imports is a concern for you, I could revert those changes. Please let me know.

Thanks in advance!

[HyukjinKwon]

It's fine since it fixes multiple instances. I see some committers are actively reviewing this.

[srowen]

Merged to master