[VPlan] Run final removeBranchOnConst after late simplifyRecipes. (#193069)
simplifyRecipes may expose additional known branches. Move final
removeBranchOnConst after the late simplifyRecipes run.
Removing branches like the vector loop backedge leads to additional
simplifications, like removing trivial phis etc. Return true if any phis
have incoming values have been removed by removeBranchOnConst. If so, we
need another simplifyRecipes run.
Depends on https://github.com/llvm/llvm-project/pull/193067 for
functional changes.
PR: https://github.com/llvm/llvm-project/pull/193069