[asan] Remove confusing workaround

The goal is to identify the bot and try to fix it.

SetSoftRssLimitExceededCallback is AsanInitInternal as I assume
that only MaybeStartBackgroudThread needs to be delayed to constructors.
Later I want to move MaybeStartBackgroudThread call into sanitizer_common.

If it needs to be reverted please provide to more info, like bot, or details about setup.

Reviewed By: kstoimenov

Differential Revision: https://reviews.llvm.org/D114934