When opening a drawing, the dialog of proxy information comes up. To turn of this dialog for future, set the system variable PROXYNOTICE to 0.
Instead of turning of the proxy information dialog box, we can clean up the drawing. Firstly, try '-PURGE' and select 'RegApps', because normal 'PURGE' doesn't purge 'RegApps'. If this doesn't work, use 'WBLOCK' and export entire drawing to a new drawing.