Remove OpenGE and related libraries
OpenGE is no longer the path forward now that Epic Games has released the UnrealBuildAccelerator.
I was going to remove it after !84 stabilizes, but there's a bug in OpenGE that prevents file copies happening on macOS when creating a packaged project for a plugin, and I don't want to spend time investigating a command line parsing bug that will be irrelevant in the near future.
Therefore, this merge request deletes OpenGE and all related code, and for now UET will not be able to observe the progress builds until !84 is merged.