Improve compat mode scaling implementation.

Rip out the old funky code for trying to restrict the app window
sizes to be within the compat mode range.  Instead, we know rely
entirely on scaling -- we deal with windows always with the scaling
applied so that the window manager doesn't have to deal with them
specially.  Instead, we just apply the inverse scale at the few
points we need to do something the app sees.

Change-Id: I785409dd4513b5f738684e1635dc8f770c249651