Remove sym center point upon building block death/delete

Remove sym center point upon building block death/delete because it is a bit annoying when it remembers the center point when the block you placed is no longer there. and if you place another building block it will make a random block as if the original building block is there trying to build symmetry off it. 

This could be possible with a single block but you could set the point over 6 blocks or 3 floors up. It’s up to the user to toggle symmetry on and off

Changed Status from Pending to Not a Bug