Extend the for loop to use all samples

Currently, the last sample is treated in a special manner (consistent
with the docs for MotionEvent).
However, the public api of MotionEvent also work fine if the element at
index [historySize] is accessed.

Therefore, calling event.getX() is the same as calling
event.getHistoricalX(historySize).

To simplify the code, remove the redundant code and instead extend the
loop by 1.

Bug: 167946721
Test: atest libinput_tests
Change-Id: Icc1fff1b0f16d63d7d0eb33e5977a3b3b440f562