BERLIN — In a landmark ruling that will make it easier for people to allow relatives and other loved ones to die, Germany’s highest court ruled Friday that it was not a criminal offense to cut off life-sustaining treatment for a patient. The court overturned the conviction of a lawyer who last year was found guilty of attempted manslaughter for advising a client to sever the intravenous feeding tube that was keeping her mother alive, although in a persistent vegetative state. The mother had told her daughter that she did not wish to be kept alive artificially.