remove multiplexing of multiple EGL implementation

from now on, the system can only have one EGL
implementation. this means the software and h/w renderer
cannot be used at the same time on a device. Of course, the
h/w renderer is always prefered; in its absence we
default to the software renderer.

Change-Id: Ib579f58055dd0ce4c4a99144131efa11c16ca3d3