Remove unneeded includes in gamemode_client.h

lib/gamemode_client.h

@@ -68,11 +68,8 @@ POSSIBILITY OF SUCH DAMAGE.
 
 #include <stdbool.h>
 #include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
 
 #include <dlfcn.h>
-#include <errno.h>
 #include <string.h>
 
 #include <sys/types.h>