Revert "buildtools: Copy lib++ headers for Clang modules build"

This reverts commit 7a8b870b60f77180dc3ab3bb3f6d6cdc5c86e148.

Reason for revert: It breaks https://ci.chromium.org/ui/p/chrome/builders/ci/android-arm/44908/overview

Original change's description:
> buildtools: Copy lib++ headers for Clang modules build
>
> This is to have libc++ headers and __assertion_handler in the same
> directory for Clang modules build.
>
> Bug: 408128305
> Change-Id: Iad590d053e7fcc7a3414ad5b6e1249126eca5b9b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6440444
> Reviewed-by: Junji Watanabe <jwata@google.com>
> Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1444568}

Bug: 408128305
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: Iaeb4e9f3c9c730dcb3ad95df0ff64497e40c9a56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6440532
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Junji Watanabe <jwata@google.com>
Cr-Commit-Position: refs/heads/main@{#1444586}