AP_Follow: remove header reliance on GCS and AHRS

libraries/AP_Follow/AP_Follow.cpp

@@ -14,11 +14,12 @@
  */
 
 #include <AP_HAL/AP_HAL.h>
-#include <GCS_MAVLink/GCS.h>
 #include "AP_Follow.h"
 #include <ctype.h>
 #include <stdio.h>
 
+#include <AP_AHRS/AP_AHRS.h>
+
 extern const AP_HAL::HAL& hal;
 
 #define AP_FOLLOW_TIMEOUT_MS    3000    // position estimate timeout after 1 second

libraries/AP_Follow/AP_Follow.h

@@ -18,7 +18,6 @@
 #include <AP_HAL/AP_HAL.h>
 #include <AP_Param/AP_Param.h>
 #include <AP_Math/AP_Math.h>
-#include <AP_AHRS/AP_AHRS.h>
 #include <GCS_MAVLink/GCS.h>
 #include <AC_PID/AC_P.h>
 #include <AP_RTC/JitterCorrection.h>