Remove WmLookup.
Since we no longer need WmLookup, WmLookup.(c|hh) and
WmLookup(Aura|Mus).(c|hh) will be removed.
The calling sites to WmLookup::GetWindowForWidget(widget) can just call
WmWindow::Get(widget->GetNativeWindow()).
The calling sites to WmLookup::GetRootWindowControllerWithDisplayId(id)
can just call Shell::GetRootWindowControllerWithDisplayId(id).
Review-Url: https://codereview.chromium.org/2726823003
Cr-Commit-Position: refs/heads/master@{#454615}
76 files changed
