[llvm] [SLP]Remove operands upon marking instruction for deletion. (PR #97409)

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dyung wrote:

Hi @alexey-bataev, we are seeing an assertion failure in internal tests which I bisected back to this change. What is odd is that it does not hit the assertion failure reliably, so there seems to be some element of randomness to it. I have put the repro and assertion failure stack trace in issue #98133. Can you take a look?

https://github.com/llvm/llvm-project/pull/97409