Revert "Model validation support"

This reverts commit 155e38f8.

Reason for revert: This culprit CL fails
PageContentAnnotationsServiceLoadEachExecutionTest.ModelLoadsAndExecutes test.

on Win bots.
https://ci.chromium.org/ui/p/chromium/builders/ci/Win7%20(32)%20Tests/71504/overview

Original change's description:
> Model validation support
>
> Introduces a ModelValidator class and adds a command-line switch to
> validate model using ModelValidator. No code is expected to run when the
> command-line switch is not specified.
>
> Bug: 1219668
> Change-Id: I12f93956b4657bb9997b772a797f1e37d2e99a03
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2999073


> Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
> Reviewed-by: Sophie Chang <sophiechang@chromium.org>
> Commit-Queue: rajendrant <rajendrant@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#908596}

Bug: 1219668
Change-Id: I82f41398cf1eab3538477d7a348588074065dc08
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3071500
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Owners-Override: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908715}