removed duplicate build file

cmake/ubuntu.cmake

-# Ubuntu Linux
-
-set(lib_base /usr/include)
-set(sdl_root ${lib_base}/SDL)
-
-include_directories("${sdl_root}")
-
-link_libraries(cannonball 
-    SDL
-    SDLmain
-)
-
-# Linking
-link_directories(
-    "${sdl_root}/lib"
-)
- 
-# Location for Cannonball to create save files
-# Used to auto-generate setup.hpp with various file paths
-set(xml_directory ./)
-set(sdl_flags "SDL_DOUBLEBUF | SDL_SWSURFACE")