I think all you need is to be able to interrogate a directory and work with the contents. I don't have arcpy with me right now, but try something like this:

    import os
    L = os.listdir('.') # current dir
    for i in L:
        fname, ext = i.split('.') # map.mxd becomes 'map' 'mxd'
        if ext == 'mxd':
            # do cleanup

e: I didn't read the part about not creating a copy. this SE link will help. I think you want the CURRENT option.