Make a litte batch file with the following line and execute it from the parent folder under which there are .svn directories.
FOR /F "tokens=*" %%G IN ('DIR /B /AD /S *.svn*') DO RMDIR /S /Q "%%G"
You can also issue the line below straight from the Command Prompt:
FOR /F "tokens=*" %G IN ('DIR /B /AD /S *.svn*') DO RMDIR /S /Q "%G"