DSP/LabelMap: Default constructor and destructor

We also move the destructor definition into the cpp file, as that will
allow us to make the entire label_t type hidden from external view in a
following change.

Source/Core/Core/DSP/LabelMap.cpp

@@ -11,9 +11,9 @@
 
 namespace DSP
 {
-LabelMap::LabelMap()
-{
-}
+LabelMap::LabelMap() = default;
+
+LabelMap::~LabelMap() = default;
 
 void LabelMap::RegisterDefaults()
 {

Source/Core/Core/DSP/LabelMap.h

@@ -23,7 +23,8 @@ class LabelMap
 {
 public:
   LabelMap();
-  ~LabelMap() {}
+  ~LabelMap();
+
   void RegisterDefaults();
   void RegisterLabel(const std::string& label, u16 lval, LabelType type = LABEL_VALUE);
   void DeleteLabel(const std::string& label);