Revert of Converts chrome to aura-mus (patchset #4 id:60001 of https://codereview.chromium.org/2578893003/ )

Reason for revert:
Broke Linux ChromiumOS Builder (dbg) build.
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Builder%20%28dbg%29/builds/81640

Original issue's description:
> Converts chrome to aura-mus
>
> aura-mus has a different environment than mus, so WMHelperMus (in exo)
> was updated accordingly.
>
> This breaks switches::kUseMusInRenderer. I'll fix that next.
>
> BUG=672932 663525
> TEST=covered by tests
> [email protected], [email protected]
>
> Committed: https://crrev.com/e3e1ea3c0699e70c8ca5a6a790641c58be4e1381
> Cr-Commit-Position: refs/heads/master@{#439044}

[email protected],[email protected],[email protected]
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=672932 663525

Review-Url: https://codereview.chromium.org/2577963006
Cr-Commit-Position: refs/heads/master@{#439063}
32 files changed