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
To delete all svn files on windows
for /d /r . %d in (.svn) do @if exist "%d" rd /s/q "%d"
.svn is the folder name