Remove ui.nsi

I can't seem to figure out what purpose the ui.nsi file serves if any.
In my tests on Windows 2008R2 not making it and even having it present
seem to make no difference in the agent functionality. The win32ui
still gets installed and everything about it still seems to work.

Getting rid of it seems like a good idea to me at this point.

If anyone can tell me if this does get used for anything and what that anything is it would be much appreciated. Further testing always welcome.