It seems to be initially added almost two years ago in commit

407f785186a43c55872cc9b5e5ab55b0a7f9b106

Now it seems to se unused for a very long time, since the pan/zoom actions
do not call the tool's event callbacks.

If one decides to resurrect this "fast-path", please revert a part of this
patch and implement either in input manager actions or (better) in
KisCanvasController panning/zooming code.