Revert "[InstCombine] keep assumption before sinking calls"

Summary:
This reverts commit c3b06d0c.

Reason for revert: Caused miscompiles when inserting assume for undef.

Also adds a test to prevent similar breakage in future.

Fixes PR44154.

Reviewers: rnk, jdoerfert, efriedma, xbolva00

Reviewed By: rnk

Subscribers: thakis, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70933