A homeless Bronx straphanger with nearly two dozen prior arrests allegedly beat and choked another vagrant to death after that man roused him from his sleep with a cane early Wednesday, prosecutors and sources said. The homeless victim — identified by prosecutors as Cranston Smith — allegedly tapped snoozing stranger Keith Plummer, 68, with the cane on board a No. 1 train at the 242nd Street-Van Cortlandt Park Station around 3 a.m. Wednesday, law enforcement sources said.  The random contact sparked a brawl between the two men – with Plummer allegedly straddling Smith, punching him multiple times and grabbing and pressing on his neck, according to a complaint filed in Bronx Criminal Court. The deadly altercation started after the homeless victim — allegedly tapped stranger Keith Plummer, 68, with the cane on board a No. 1 train at the 242nd Street-Van Cortlandt Park Station around 3 a.m.…