Cleanup #includes of (mostly a long time) unused header files.

No functional changes.

src/lib/commands/lboard.c

@@ -31,14 +31,11 @@
  *     Steve McClure, 1998
  */
 
-#include <math.h>
 #include "misc.h"
 #include "player.h"
 #include "file.h"
 #include "sect.h"
 #include "path.h"
-#include "news.h"
-#include "treaty.h"
 #include "nat.h"
 #include "xy.h"
 #include "land.h"
@@ -46,7 +43,6 @@
 #include "mission.h"
 #include "ship.h"
 #include "combat.h"
-#include "retreat.h"
 #include "commands.h"
 
 int