Revert of Fix Clang update step on Windows after LLVM r242705 (patchset #2 id:20001...

Revert of Fix Clang update step on Windows after LLVM r242705 (patchset #2 id:20001 of https://codereview.chromium.org/1214863018/)

Reason for revert:
This might no longer be necessary according to cbieneman. Reverting to give that a try.

Original issue's description:
> Fix Clang update step on Windows after LLVM r242705
>
> tools/CMakeLists.txt upstream has been updated to be more clever
> and automagic about how it picks up dependencies to build in
> tools. Unfortunately, this means that the clang target was not
> defined before chrometools, which led to build errors.
>
> BUG=507826

TBR=dcheng@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=507826

Review URL: https://codereview.chromium.org/1255723002

Cr-Commit-Position: refs/heads/master@{#340163}