Revert back to NOT use those generated csproj, to prove that it's not me who broke build...

Now Rx_Android.sln fails to build with the following error:
https://gist.github.com/82b0c92263b53cf0f793

This smells like a smcs or runtime error. monodevelop successfully resolves
those types on the tooltip, so the full mono (from some old master) works.