This reverts commit 7f054679.

Reason for revert: regressions on Emscripten/Fannkuch and
JetStream/richards

Original change's description:
> [regalloc] Run SpillPlacer on any value defined in a loop
> 
> I previously wrote a comment that said "We haven't seen any indication
> of performance improvements from seeking optimal spilling positions
> except on loop-top phi values". That statement is no longer true, now
> that I've looked a little harder. In the latest version of the Mono
> interpreter, we can improve performance by 2.5% by enabling SpillPlacer
> for any value defined within a loop.
> 
> Bug: v8:10606
> Change-Id: I25e06458c87ad4ffcefe52be3042032e05a47b35
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2381557
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
> Cr-Commit-Position: refs/heads/master@{#69646}

TBR=rmcilroy@chromium.org,seth.brenith@microsoft.com,thibaudm@chromium.org

Change-Id: Ic3e74485f42bafedfe1890c0be32a29c3455afe5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:10606, chromium:1124028
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2388745Reviewed-by: Seth Brenith <seth.brenith@microsoft.com>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#69658}