Revert "Upgrade the default scroll distance to 120"

This was part of the high-resolution wheel work that was factored out ahead of
time. Problem is: this breaks scroll button emulation in the server as we
use the distance to determine when we click buttons 4-7.

Before: movement of 15 normalized pixel units on a touchpad - one click. Now:
120 of those units. So that's a bit less than ideal.

The change to 120 can be done, but needs the corresponding handling in the
axis distance calculations.

Fixes #24

This reverts commit 05548118.