GCS_MAVLink: use mission singleton

libraries/GCS_MAVLink/GCS.h

@@ -279,7 +279,6 @@ protected:
     // overridable method to check for packet acceptance. Allows for
     // enforcement of GCS sysid
     virtual bool accept_packet(const mavlink_status_t &status, mavlink_message_t &msg) { return true; }
-    virtual AP_Mission *get_mission() = 0;
     virtual AP_Rally *get_rally() const = 0;
     virtual AP_AdvancedFailsafe *get_advanced_failsafe() const { return nullptr; };
     virtual AP_VisualOdom *get_visual_odom() const { return nullptr; }

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -2997,7 +2997,7 @@ void GCS_MAVLINK::handle_common_message(mavlink_message_t *msg)
 
 void GCS_MAVLINK::handle_common_mission_message(mavlink_message_t *msg)
 {
-    AP_Mission *_mission = get_mission();
+    AP_Mission *_mission = AP::mission();
     if (_mission == nullptr) {
         return;
     }
@@ -3527,7 +3527,7 @@ bool GCS_MAVLINK::try_send_compass_message(const enum ap_message id)
 
 bool GCS_MAVLINK::try_send_mission_message(const enum ap_message id)
 {
-    AP_Mission *mission = get_mission();
+    AP_Mission *mission = AP::mission();
     if (mission == nullptr) {
         return true;
     }

libraries/GCS_MAVLink/GCS_Dummy.h

@@ -24,7 +24,6 @@ class GCS_MAVLINK_Dummy : public GCS_MAVLINK
 
 protected:
 
-    AP_Mission *get_mission() override { return nullptr; }
     AP_Rally *get_rally() const override { return nullptr; };
 
     uint8_t sysid_my_gcs() const override { return 1; }

libraries/GCS_MAVLink/examples/routing/routing.cpp

@@ -30,7 +30,6 @@ public:
 protected:
 
     uint32_t telem_delay() const override { return 0; }
-    AP_Mission *get_mission() override { return nullptr; }
     AP_Rally *get_rally() const override { return nullptr; }
     uint8_t sysid_my_gcs() const override { return 1; }
     bool set_mode(uint8_t mode) override { return false; };