The current `Snap Base` was available and displayed to allow snapping
to `Edge Perpendicular`.
However, the usefulness of perpendicular snapping in `Set Snap Base`
mode is questionable and can sometimes cause inconvenience.
Also, removing the current `Snap Base` indicator (the `X` drawing)
makes the intention of the operation more apparent.
Therefore, this commit removes both the indicator and the effect of the
current `Snap Base` in `Set Snap Base` mode.
Germano Cavalcante