acqEngine: Remove rogue references to the gui's position list

In particular, when null is passes as the position list argument to
run(), the gui's position list should never be consulted.

Also removed functions that modify the position list but are never
called.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14500 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd
acqEngine: Fix exposure-interval criterion for hardware triggering

When channels are in use, the camera's initial exposure should have no
effect on whether timepoints are combined into bursts.

Regression test added.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14501 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd
Revert r14065 "listen to core callbacks for Z stage and XY stage"

As discussed in correspondence between Arthur and Mark, this has the
danger of taking an intermediate (in-motion) value for the stage
positions and recording it, because there is no guarantee about the
timing of position change notifications from the device.

Reverting until a better solution is found.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14502 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd