The removed flags are:

1. --turbo-nci-as-midtier
2. --turbo-nci-cache-ageing
3. --turbo-nci-delayed-codegen

Flag 1. was used by a testing mode that is no longer used. Flags 2. and
3. were used to experiment with codegen and cacheing heuristics, no
longer needed now that work is suspended.

Bug: v8:8888
Change-Id: Ib4a89f09340c2d94ee7688928c8235276c1f1032
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2661461
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72476}