DC++ 0.75+1 Drops ADC/0.10 Compatibility

DC++ pre-0.704 and DC++ 0.75+1 cannot communicate via client-client ADC connections to transfer files. This change affects neither ADCS/0.10 nor NMDC client-client protocol-based interoperability. Anyone using using a DC++ client recent enough to have even moderate ADC support but old enough to be directly affected by this should have already updated to at least DC++ 0.707 to avoid remotely triggerable crashes, regardless.