Remove double initialization of the inut manager on image creation

The initialization in KisCanvas2::setCanvasWidget() was intended only
for the case when the canvas type is switched (opengl<->qpainter) and
it shouldn't trigger during normal canvas creation process.

This patch is too dangerous for 4.3.0 release, it should be pushed into
4.3 branch only for 4.3.1 release.

BUG:421518