You're supposed to be able to customise the xml file for the style to remove that.
For example, see:
http://msdn.microsoft.com/en-us/library/office/jj851016(v=office.15).aspx
or
http://blogs.office.com/2009/04/29/bibliography-citations-102-building-custom-styles/
However, I have looked at some of those file, and they are, to me, confusing messes.
I would recommend rather using Yves Dhondt's rather brilliant little tool, BibWord:
http://bibword.codeplex.com/
It's much easier to change these settings there, and there are a number of Harvard-type styles that might already suit your purposes.