[llvm-reduce] Reducing call operand bundles

Summary:
This would have been marginally useful to me during/for rG7ea46aee3670981827c04df89b2c3a1cbdc7561b.

With ongoing migration to representing assumes via operand bundles on the assume, this will be gradually more useful.

Reviewers: nickdesaulniers, diegotf, dblaikie, george.burgess.iv, jdoerfert, Tyker

Reviewed By: nickdesaulniers

Subscribers: hiraditya, mgorny, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D83177