starter: Ensure the daemon executable exists when starting up

The only purpose of starter is to control the IKE daemon, so we
terminate it if the daemon executable is not found (e.g. because
DAEMON_NAME is incorrect).

This removes the charonstart setting (it was not actually configurable
anymore).

src/starter/confread.h

@@ -193,7 +193,6 @@ typedef struct starter_config starter_config_t;
 
 struct starter_config {
 		struct {
-				bool     charonstart;
 				char     *charondebug;
 				bool     uniqueids;
 				bool     cachecrls;