On a Windows system since you mention DOS, open a command prompt at the root of the directory structure you saved your files to (hopefully, you are not trying to do this to your calibre library as that is very ungood).
Then enter "del /s /q *.opf" and once that command completes enter "del /s /q *.jpg". Or you could put both lines into a .cmd file. The first line changes to the drive and directory which is the root of your exported file directories.
Something like;
Code:
cd /d "e:\root of file storage"
del /s /q *.opf
del /s /q *.jpg
pause