[Attributor] [NFC] Use `checkForAllUses` helpr in `AAHeapToStackImpl::updateImpl`

Summary: Remove `Worklist` iteration and make use `checkForAllUses`. There is no test chage.

Reviewers: sstefan1, jdoerfert

Reviewed By: jdoerfert

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71352