Fix warnings (#3852)

* Remove register keyword

Register is meaningless in c++, and removed in c++17

* Fix compiler warningsg

Add missing override, remove unused capture, and remove unused local variablees

include/BBTrackContainer.h

@@ -41,9 +41,9 @@ public:
 	virtual bool play( MidiTime _start, const fpp_t _frames,
 						const f_cnt_t _frame_base, int _tco_num = -1 );
 
-	virtual void updateAfterTrackAdd();
+	virtual void updateAfterTrackAdd() override;
 
-	inline virtual QString nodeName() const
+	inline virtual QString nodeName() const override
 	{
 		return "bbtrackcontainer";
 	}