ENH: display unload filament button when use_ams is false

Change-Id: I4dc7cc17c33e5f92543934c3d003c34fea94b0cb
Signed-off-by: Stone Li <stone.li@bambulab.com>

src/slic3r/GUI/DeviceManager.hpp

@@ -439,6 +439,7 @@ public:
     // parse amsStatusMain and ams_status_sub
     void _parse_ams_status(int ams_status);
     bool has_ams() { return ams_exist_bits != 0; }
+    bool can_unload_filament();
     bool is_U0_firmware();
     bool is_support_ams_mapping();
     bool is_only_support_cloud_print();