rcfile: when rebound, DO unbind a keystroke from its earlier function

When not unbinding it from its earlier function (in the same menu),
it would result in showing the keystroke twice in the help text.

This fixes https://savannah.gnu.org/bugs/?55239.

Bug was introduced a month ago, by commit f81d174f.

src/rcfile.c

@@ -428,12 +428,12 @@ void parse_binding(char *ptr, bool dobind)
 		goto free_things;
 	}
 
-	/* When unbinding, wipe the given shortcut from the given menu. */
-	if (!dobind) {
+	/* Wipe the given shortcut from the given menu. */
 	for (s = sclist; s != NULL; s = s->next)
 		if ((s->menus & menu) && strcmp(s->keystr, keycopy) == 0)
 			s->menus &= ~menu;
 
+	if (!dobind) {
   free_things:
 		free(newsc);
 		free(keycopy);