Yes as the data isn't there, but in the data file where they are stored, see below. Again I have no idea why you would want to do this or what you are trying to achieve by doing this as you aren't going to be saving large amounts of disk space.
C:\Documents and Settings\All Users\Application Data\Alwil Software\Avast5\report\WebShield.txt XP location, differs for Vista and win7.
The whole point of the web shield is to detect malware on web sites and stop it getting on to your system (it aborts the connection, dropping that infected item), all it is doing is recording the information on the detection ( as I said in my first reply "they don't retain copies of the web files relating to the detection." So it isn't on your system, it is just historic data.