Open a patch file in a text editor and you'll find it's nothing more than
- Which file
- What to add on which line (indicated by
- What to remove on which line (indicated by
So you could do it manually. But the kind folks of Magento also included a
Revert option in the patch files. If you check the
usage menu you'll find it.
Usage: sh $BASE_NAME [--help] [-R|--revert] [--list]
Apply embedded patch.
-R, --revert Revert previously applied embedded patch
--list Show list of applied patches
--help Show this help message
Now before you start reverting that stuff
The patches are there for a reason, generally a security issue. So instead of removing them fix whatever is not working to work together WITH the security patch.
And honestly. If a security patch broke a functionality it's probably because the functionality is doing things it shouldn't be doing that way in the first place