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.
Merge pull request #118 from awiddersheim/fix_win32_ui_install

Remove ui.nsi