Move extern forward decls from cpps to headers

src/d/actor/d_a_tbox.cpp

@@ -5,6 +5,7 @@
 
 #include "d/dolzel_rel.h" // IWYU pragma: keep
 #include "d/actor/d_a_tbox.h"
+#include "d/d_npc.h"
 #include "d/res/res_dalways.h"
 #include "JSystem/JUtility/JUTAssert.h"
 #include "d/d_bg_s_acch.h"
@@ -31,8 +32,6 @@
 #define FUNC_TYPE_EXTRA_SAVE_INFO 7
 #define FUNC_TYPE_EXTRA_SAVE_INFO_SPAWN 8
 
-extern dCcD_SrcCyl dNpc_cyl_src;
-
 static daTbox_HIO_c l_HIO;
 
 static daTbox_c::modelInfo l_modelInfo[] = {