move struct propname to a header file

In doing so, avoid repeated layout declaration in cmd.c

include/timeout.h

@@ -60,4 +60,9 @@ typedef struct fe {
     Bitfield(needs_fixup, 1); /* does arg need to be patched? */
 } timer_element;
 
+struct propname {
+    int prop_num;
+    const char *prop_name;
+};
+
 #endif /* TIMEOUT_H */

src/cmd.c

@@ -1952,10 +1952,7 @@ static int
 wiz_intrinsic(void)
 {
     if (wizard) {
-        extern const struct propname {
-            int prop_num;
-            const char *prop_name;
-        } propertynames[]; /* timeout.c */
+        extern const struct propname propertynames[]; /* timeout.c */
         static const char wizintrinsic[] = "#wizintrinsic";
         static const char fmt[] = "You are%s %s.";
         winid win;

src/timeout.c

@@ -21,10 +21,7 @@ static void cleanup_burn(ANY_P *, long);
 
 /* used by wizard mode #timeout and #wizintrinsic; order by 'interest'
    for timeout countdown, where most won't occur in normal play */
-const struct propname {
-    int prop_num;
-    const char *prop_name;
-} propertynames[] = {
+const struct propname propertynames[] = {
     { INVULNERABLE, "invulnerable" },
     { STONED, "petrifying" },
     { SLIMED, "becoming slime" },