Revert of Fix bitfield enums to not trigger upcoming Clang warning (patchset #3 id:40001 of https://codereview.chromium.org/2349153002/ )

Reason for revert:
Causes warning in GCC.

Original issue's description:
> Fix bitfield enums to not trigger upcoming Clang warning
>
> Fix bitfield enums to not trigger upcoming Clang warning regarding
> non-unsigned enum bitfields producing non-portable code.
>
> For more details, see the patch here: https://reviews.llvm.org/D24289
>
> BUG=648462
>
> Committed: https://crrev.com/a81e00d533454a7179f8f954505a8f033e941a8a
> Cr-Commit-Position: refs/heads/master@{#39649}

TBR=jochen@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=648462

Review-Url: https://codereview.chromium.org/2361013003
Cr-Commit-Position: refs/heads/master@{#39663}