Revert r357256 "[DAGCombine] Improve Lifetime node chains."

As it caused a pathological compile-time regressionin V8, see PR41352.

> Improve both start and end lifetime nodes chain dependencies.
>
> Reviewers: courbet
>
> Reviewed By: courbet
>
> Subscribers: hiraditya, llvm-commits
>
> Tags: #llvm
>
> Differential Revision: https://reviews.llvm.org/D59795

This also reverts the follow-up r357309:

> [DAGCombiner] Rewrite ImproveLifetimeNodeChain to avoid DAG loop.
>
> Avoid EXPENSIVE_CHECK failure. NFCI.

llvm-svn: 357563