Fix PYTHONPATH whitespace issue on Windows (see #11989).

This PR fixes http://trac.openmicroscopy.org.uk/ome/ticket/11989 by removing the call to ``setpythonpath.bat`` from ``omero.bat``. There are [numerous](http://stackoverflow.com/questions/535975/dealing-with-quotes-in-windows-batch-scripts), [hard-to-predict](http://stackoverflow.com/questions/473117/pass-path-with-spaces-as-parameter-to-bat-file) [behaviours](http://chrisoldwood.blogspot.co.uk/2013/06/handling-paths-with-spaces-parenthesis.html) with the ``FOR`` construct and paths containing spaces and parentheses. There might be scope for improving the error reported by ``setpythonpath.bat``.

To test: verify that the server starts up on Windows and that all services (thumbnail generation, search etc.) work as expected.