Copter: make wp_distance static

removed hack with AP_Camera library

ArduCopter/ArduCopter.pde

@@ -494,8 +494,8 @@ static int32_t original_wp_bearing;
 static int32_t home_bearing;
 // distance between plane and home in cm
 static int32_t home_distance;
-// distance between plane and next waypoint in cm.  is not static because AP_Camera uses it
-uint32_t wp_distance;
+// distance between plane and next waypoint in cm.
+static uint32_t wp_distance;
 // navigation mode - options include NAV_NONE, NAV_LOITER, NAV_CIRCLE, NAV_WP
 static uint8_t nav_mode;
 // Register containing the index of the current navigation command in the mission script