dselect: Remove bogus falliblesubprocess prototype and make it static

dselect/dselect.h

@@ -179,7 +179,4 @@ typedef urqresult urqfunction(void);
 urqfunction urq_list, urq_quit, urq_menu;
 urqfunction urq_setup, urq_update, urq_install, urq_config, urq_remove;
 
-urqresult falliblesubprocess(const char *exepath, const char *name,
-                             const char *const *args);
-
 #endif /* DSELECT_H */

dselect/method.cc

@@ -136,7 +136,7 @@ static enum urqresult lockmethod(void) {
   return urqr_normal;
 }
 
-urqresult
+static urqresult
 falliblesubprocess(struct command *cmd)
 {
   pid_t c1;