Revert "[cpuinfo] Set CPUINFO_MOCK in MSan builds"

This reverts commit d81424c1.

Reason for revert:
A new version of Clang which fixes the MSan problem has landed (see bug).

Original change's description:
> [cpuinfo] Set CPUINFO_MOCK in MSan builds
>
> cpuinfo is currently broken in MSan builds (see bug). Mock it until we
> find a fix.
>
> Bug: 331926164
> Change-Id: I01e23fd7315388acec32e840c2068a1667a4602b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5417594


> Owners-Override: Munira Tursunova <moonira@google.com>
> Commit-Queue: Munira Tursunova <moonira@google.com>
> Auto-Submit: Hans Wennborg <hans@chromium.org>
> Reviewed-by: Munira Tursunova <moonira@google.com>
> Cr-Commit-Position: refs/heads/main@{#1281764}

Bug: 331926164
Change-Id: Ic78585707bf84a3fe1cf8dd201fd47f0eb60bac5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5434076


Owners-Override: Mikel Astiz <mastiz@google.com>
Reviewed-by: Munira Tursunova <moonira@google.com>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1283922}