Revert "Set o.e.j.c.compiler.problem.nullUncheckedConversion to ignore by default"

[agriffis]

Hello! This pull request reverts commit 6d8eb7a3677d014fdcf3c4761706832a24f9e68c.

I don't fully understand the problem/solution in this area. What I know:

• You want to avoid a warning as @snjeza explains here

• But jdtls forcing this is overwriting Eclipse settings that are saved to the repo, as shown here

I'm hoping to either get a better explanation of why it's okay to overwrite this setting, or if perhaps there is a better solution to the earlier problem. Thank you for your patience!

[eclipse-ls-bot]

Can one of the admins verify this patch?

[agriffis]

Hello! This continues to be a problem for me, with jdtls overwriting our project settings. Is there a way I could get someone's attention to consider merging this fix?

[agriffis]

Closing in favor of #3472