Refactor blocks to not use the 'active' system

This removes the variables obj.nblocks, as well as removing the 'active'
attribute from the block object. Now every block is guaranteed to be
real without having to check the 'active' variable.

Removing a block while iterating now uses the removeblock_iter() macro.

desktop_version/src/BlockV.cpp

@@ -7,7 +7,6 @@ blockclass::blockclass()
 
 void blockclass::clear()
 {
-	active = false;
 	type = 0;
 	trigger = 0;