I have been able to remove some proxy graphics by the following method:
1. Go to your tools>options tab
2. Then open the "open and save" tab.
3. Change the "Demand Load OjbectsARXapps" setting to "Disable Load on Demand"
4. Close and re-open Autocad.
5. Open a file with those Proxy graphics in it.
6. Type in the command -wblock. Then type a new file name. This will be (hopefully") the new clean file.
7. At the prompt type a * for everthing.
8. Hopefully the new file don't have the proxy's in it.
IDK....maybe worth a try?
Remember to set the "Demand Load OjbectsARXapps" setting back to what it was, and close and re-open Autocad.