This reverts commit 14b424c3.

Reason for revert: Regresses benchmarks, e.g., Octane/gameboy

Original change's description:
> [turbofan] Lower monomorphic loads during graph building.
> 
> We introduce an explicit LoweringResult data structure. Until this change,
> the lowering result could be recovered from the node. However, lowering
> monomorphic loads requires wiring different value and effect, so we need
> a structure that can express such lowering result.
> 
> Bug: v8:6357
> Change-Id: I92655800890b744d9203a778a1936a8dcd465ed3
> Reviewed-on: https://chromium-review.googlesource.com/637304
> Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#47992}

TBR=mstarzinger@chromium.org,jarin@chromium.org,bmeurer@chromium.org

Change-Id: I2b7db0278c13414e20c94a34d215ed92bd0d412b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6357
Reviewed-on: https://chromium-review.googlesource.com/667016Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48012}