Revert "[VPlan] Add & use VPValue operands for VPWidenRecipe (NFC)."

This reverts commit 9245c7ac.

This is triggering a segfault in XLA downstream, we'll follow-up with
a reproducer, it is likely influenced by TTI/TLI settings or other
options as a simple `opt -loop-vectorize` invocation on the IR
before the crash does not reproduce immediately.