We now use the display connection specified in EglWindowInfo
throughout the EGL backend, instead of opening new connections
in EglGraphicsMode. This fixes EGL errors in
Egl.CreateWindowSurface.
As part of this fix, all instances of
IPlatformFactory.CreateGraphicsMode() have been removed. This
API is no longer used in OpenTK 1.1
* EglContext.cs:
* EglGraphicsMode.cs: Added a parameter to indicate which ES renderer
version we wish to use. Fixes issue [#2247]: "CreateEGLGraphicsMode
should select the correct renderer".