In order to delete all \".svn\" files/folders/subfolders in \"myfolder\" I use this simple line in a batch file:
FOR /R myfolder %%X IN (.svn) DO (RD /S /Q \"%%X
for /f "tokens=* delims=" %%i in ('dir /s /b /a:d *svn') do (rd /s /q "%%i")