We don't need to update the source's capabilities when setting our
output state. Now we just send a new Request. For now, that request is
redundant, but soon I want to make the Sink request less current when
the output is disabled. Whether the voltage should be the same or
always vSafe5V in that case, I haven't decided yet. There are
advantages to each, but the difference is so minor in terms of using the
device that I don't see a reason to let the user choose, which of course
puts the decision on me.