don't return pc in transition methods; just modify QAM state about qvm HOT 1 CLOSED

Adding context at the request of @rigettizach.

This issue isn't a bug, but an improvement in matching the machine model of the quantum abstract machine. The program counter is a piece of state in the machine, and the way it's described in the Quil paper is modification of this state.

The fact that qvm::transition modifies some state but not the pc is misleading, and also doesn't reflect what a real quantum computer does.

This issue is supposed to make the modification of state more uniform. The transition method currently returns the updated pc as a second value, but we ought to just transition the QAM as a state transition.

from qvm.