Give deltax(), deltay() internal linkage

External linkage unnecessary since commit 3ca88271.

include/prototypes.h

@@ -280,8 +280,6 @@ extern int logreopen(void);
 extern void logerror(char *, ...) ATTRIBUTE((format (printf, 1, 2)));
 /* more in misc.h */
 /* mapdist.c */
-extern int deltax(int, int);
-extern int deltay(int, int);
 extern int mapdist(int, int, int, int);
 /* move.c */
 /* in path.h */

src/lib/common/mapdist.c

@@ -31,17 +31,13 @@
  *
  */
 
-/*
- * mapdist returns (integer) distance between two sectors.
- */
-
 #include <config.h>
 
 #include "misc.h"
 #include "optlist.h"
 #include "prototypes.h"
 
-int
+static int
 deltax(int x1, int x2)
 {
     int dx;
@@ -53,7 +49,7 @@ deltax(int x1, int x2)
     return dx;
 }
 
-int
+static int
 deltay(int y1, int y2)
 {
     int dy;