<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def remove_tmp_prefix_from_filename(filename):
 """ Remove tmp prefix from filename. """

    if not filename.startswith(dju_settings.DJU_IMG_UPLOAD_TMP_PREFIX):
        raise RuntimeError(ERROR_MESSAGES['filename_hasnt_tmp_prefix'] % {'filename': filename})
    return filename[len(dju_settings.DJU_IMG_UPLOAD_TMP_PREFIX):]