This reverts commit b1769313.

Reason for revert: Flag access breaks TSAN (not an issue with this
CL as such, but we need to revert to re-open the tree).

Original change's description:
> [regalloc] Introduce deferred fixed ranges
> 
> Fixed ranges are used to express register constraints in the
> allocator. This change splits these fixed ranges into one for
> normal code and deferred code. The former are handeled as before
> whereas the latter are only made visible while allocating
> registers for deferred code.
> 
> This prevents forward looking decisions in normal code to be
> impacted by register constraints from deferred code.
> 
> Change-Id: I67d562bb41166194e62765d5ab051bc961054fc7
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1477742
> Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#60322}

TBR=jarin@chromium.org,sigurds@chromium.org,herhut@chromium.org

Change-Id: I5675a96acf0b5e5f7d63c60a742d2971b6d0d34d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1530803Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60324}