Remove star import of the packages, which contain conflicting declarations

[mvicsokolova]

Star imports of java.util.concurrent.atomic.* and kotlin.concurrent.* will lead to the compilation error: once Atomic classes are introduced in kotlin.concurrent package, they will conflict with Java atomic classes, which have the same names.

[mvicsokolova]

And I'll need this commit in kotlin-community/dev branches too, when we merge it)

[dkhalanskyjb]

git grep -lF 'kotlin.concurrent.*' | xargs git grep -lF 'java.util.concurrent.atomic.*' confirms that only this file has both of the star imports.

Normally, I'd ask for a comment near the import (so as to avoid accidentally reverting the change), but in this case, the stakes don't seem high: in the worst case, the CI will fail, but we'll likely upgrade to the new atomics before we touch the file for any reason, so even that is far-fetched.

We can merge this once the CI passes.