This reverts commit e38cb757.

Reason for revert: Test failing: https://logs.chromium.org/logs/v8/buildbucket/cr-buildbucket.appspot.com/8858103866497469056/+/steps/Check/0/logs/tier-down-to-liftoff/0

Original change's description:
> [turboprop] Enable tierup to TurboFan with FLAG_turboprop
>
> FLAG_turboprop was used to test the turboprop compiler without any
> further tierup to TurboFan. This cl changes:
> - FLAG_turboprop to also tier up to TurboFan.
> - Introduces FLAG_turboprop_as_toptier to continue running the
>   configuration without tierup.
> - Removes FLAG_turboprop_as_midtier which is same as FLAG_turboprop.
>
> Bug: v8:9684
> Change-Id: I487bda13d226434837770ecc43b3ced7c31ccf19
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2622214
> Commit-Queue: Mythri Alle <mythria@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#72101}

TBR=rmcilroy@chromium.org,mythria@chromium.org,jgruber@chromium.org

Change-Id: Ic3e87c311fba001460e4f1561a2e5f74391a06a7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:9684
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2630526Reviewed-by: Francis McCabe <fgm@chromium.org>
Commit-Queue: Francis McCabe <fgm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72102}