Eliminate duplicate device creation code

On startup, SurfaceFlinger used a special code path to set up the
primary display.

This removes the code, as all display event processing is done on
initialization, so the normal DisplayDevice creation path is used.

This also resolves some differences between the two code paths so the
primary display is set up the same way.

Bug: 38464421
Test: Settings app is navigable.
Change-Id: Icef8ee6c2ddd26604a33f06fb45ec0a743d82a29