Clear highlights after moving piece in Edit Position

Clear highlights after moving piece in Edit Position

When moving a piece during Edit position the from-square remained
highlighted, but the to square was not highlighted, which would
create the erroneous impression that the (now-empty) from-square
was selected (and ready to obliterate a piece on the next click).
Now this highlight is cleared. This was preferred over also highlighting
the to-square, because this is not really a move in a game.