Remove unused private members.
Remove unused private members.
Remove unused private members.

Also removes the now unused SPACE_CONSUMPTION enum.
Remove a useless cast.
Remove a useless cast.
Remove a useless cast.
Disable null conversion warning in CMake.

It gives problems when using Clang and boost::shared_ptr when compiling
for C++11. The issue can't be fixed since Wesnoth uses C++98. (So we use
NULL instead of nullptr.)