Removes unit from group, returns true on success; returns false on failure (no operation).
If unit is null, does nothing and returns false regardless if there're null values at any index in the group (does not remove destroyed units which are still in group).
Removes unit from group, returns true on success; returns false on failure (no operation).
If unit is null, does nothing and returns false regardless if there're null values at any index in the group (does not remove destroyed units which are still in group).