Override VelocityTracker strategy for non-differential axes only

VelocityTracker may use different strategies, depending on the system
flags. By default, the behaviour is like this:
AXIS_X -> lsq2
AXIS_Y -> lsq2
AXIS_SCROLL -> impulse

However, if we provide a specific strategy to VT, then things would
change. The new map would look like this:
AXIS_X -> provided strategy
AXIS_Y -> provided strategy
AXIS_SCROLL -> provided strategy

This works fine if the user specifies "impulse" as the desired strategy,
because impulse supports all of the axes.
However, lsq2 only works in non-differential mode.

The combination of "AXIS_SCROLL -> lsq2" is not allowed.

To fix this, we only allow the specified strategy to affect
non-differential axes.

This is fine, because currently, impulse is the only strategy that can
work in the differential mode.

To reproduce the issue:
1. Run `atest VelocityTrackerTest`. Test should pass, because the
   default strategy is being used.
2. Connect the device to internet
3. Reboot the device
4. Run `atest VelocityTrackerTest` again. Test should fail because the
   device would pick up an "lsq2" strategy value and then try to run the
   axis_scroll tests with it.

Bug: 295290374
Test: atest VelocityTrackerTest
Change-Id: I702a2a3e58db3ce2e0ff0c33122839a527eebab2