fix tracker module eta index calculation

This MR fixes the tracker module mapping such that it matches the desired mapping found on page 4 here. Where this quote from Dave then explains how the eta and phi indices should be calculated:

It is a rule in the offline software that indices increase in the same direction as the global coordinates in a right-handed system with +z downstream and +y (nearly) opposite gravity. So the eta = -1 corresponds to negative X (to the right, when looking downstream), and eta = +1 corresponds to positive X (to the left, when looking downstream). Similarly, the phi module index increases in the upward vertical direction, with phi = 0 closest to the floor.

This results in the correct mapping (module,phi,eta) being: (0,3,1) (1,2,1) (2,1,1) (3,0,1) (4,3,-1) (5,2,-1) (6,1,-1) (7,0,-1)

The old code was calculating the eta index wrong and was thus flipping the tracker modules over X and inverting the X direction of the tracker. It was also first converting the online module number to an offline module number (a relic of how the code worked years ago) before calculating the phi and eta indices. In this MR, i remove the useless and confusing conversion and just calculate the indices directly from the online module number.