As I'm sure all of you have found there are lots of helpful articles out there about how to do a silent install of Microsoft Office/Project/Visio/etc through SCCM, but there is very little information out there on how to do an un-install silently. After much head scratching I finally found the method of doing so...
1. Navigate to the directory where your install files are located
2. Edit the config.xml file located within prjstd.ww (note this changes depending on the version of Project)
3. Remove the values from the Display level line and change it to look like below
4. Within your SCCM deployment modify the Uninstall file to read:
setup.exe /uninstall prjstd /config prjstd.ww/config.xml (again note the visio version name will differ depending on the edition)
5. Click OK and test the uninstallation via SCCM software centre