Revert "[clang] Make update.py verify that the expected and real versions match"

This reverts commit dc9652a8.

Reason for revert:
It breaks building new packages: https://ci.chromium.org/ui/p/chromium/builders/try/mac_upload_clang_arm/920/overview

Original change's description:
> [clang] Make update.py verify that the expected and real versions match
>
> To fix problems when building with a new version of update.py without
> having run 'gclient sync', which could e.g. lead to PCH files built with
> the wrong clang version being left in the tree (see bug).
>
> Bug: 608105
> Change-Id: Ia5b70506be3f6a89d17742b6b2e0bf3271585d31
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3847019


> Commit-Queue: Hans Wennborg <hans@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1038229}

Bug: 608105
Change-Id: Iba0891530aa452b7ce773f00438ccaa62ce86988
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3851921


Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1038345}