clang-tidy: partially fix readability-redundant-declaration

src/modules/load_mon/load_mon.cpp

@@ -56,8 +56,6 @@
 #  error load_mon support requires CONFIG_SCHED_INSTRUMENTATION
 #endif
 
-extern struct system_load_s system_load;
-
 #define STACK_LOW_WARNING_THRESHOLD 300 ///< if free stack space falls below this, print a warning
 #define FDS_LOW_WARNING_THRESHOLD 3 ///< if free file descriptors fall below this, print a warning
 

src/modules/mavlink/mavlink_main.cpp

@@ -85,8 +85,6 @@ static Mavlink *_mavlink_instances = nullptr;
  */
 extern "C" __EXPORT int mavlink_main(int argc, char *argv[]);
 
-extern mavlink_system_t mavlink_system;
-
 void mavlink_send_uart_bytes(mavlink_channel_t chan, const uint8_t *ch, int length)
 {
 	Mavlink *m = Mavlink::get_instance(chan);