As Flash Pro CS 5.5 and later can read any future version, and generally Flash only saved back two versions, the save as feature was dropped after CS6. If you want to take a CC version file back to CS5, you need to go via either CS5.5 or CS6. Either of those can open the CC file, and do a save as to CS5.
It's almost four years since CS5.5 came out, hopefully most people will have changed from CS5 since then.
BTW, you don't need to save as XFL when going via CS5.5, it can read CC FLA files ok.