Revert "[clang] Build clang with pinned clang on all platforms"

This reverts commit e4598f8d5c0b63528f3b1450aaeafcefe2ddd8ad.

Reason for revert: breaks ToT win bots, e.g. https://ci.chromium.org/ui/p/chromium/builders/ci/ToTWin/1391/overview

Original change's description:
> [clang] Build clang with pinned clang on all platforms
>
> Followup to https://crrev.com/c/3572241.
>
> We can't use NamedTemporaryFile on Windows (can't read from it while having a handle to it): https://docs.python.org/3.9/library/tempfile.html. Use a consistent path for the pinned update.py instead.
>
> Bug: 1010466, 1013560
> Change-Id: Ibaa0e7d2e9789ac24a852f3c7083a59cb242e793
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3590911
> Reviewed-by: Hans Wennborg <hans@chromium.org>
> Commit-Queue: Arthur Eubanks <aeubanks@google.com>
> Cr-Commit-Position: refs/heads/main@{#997580}

Bug: 1010466, 1013560
Change-Id: Ia71a175de39d73aaa217fdf4e53df5d17b1cef84
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3616878
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Arthur Eubanks <aeubanks@google.com>
Auto-Submit: Arthur Eubanks <aeubanks@google.com>
Cr-Commit-Position: refs/heads/main@{#997944}
NOKEYCHECK=True
GitOrigin-RevId: f2a968f6513167caf5335dfbe6c29123675168af
2 files changed