You don't say what type of switches , on IOS switches you can see who did the last update by using "show vtp status" , this will give the last server that updated the vtp info. If you have more than 1 server it will not tell you that and no easy way to tell without logging into each switch and looking at the config. If the vlans are advertised in a client server setup the only place you can get rid of vlans is at the server side because these are the ones advertising the vlans...