Fix windows build...

Defaulted move constructors and assignments introduced at 080dd34 are not
essential but might give a bit more efficiency in std::vector on non-Windows.

Previous compilation fix was incorrect!  Excpliticly defined move assignments
should not have had no-effect bodies!

src/Lyrics.h

@@ -28,8 +28,8 @@ struct Syllable {
    Syllable() = default;
    Syllable( const Syllable& ) = default;
    Syllable& operator= ( const Syllable& ) = default;
-   Syllable( Syllable && ) {}
-   Syllable& operator= ( Syllable&& ) { return *this;}
+   //Syllable( Syllable && ) = default;
+   //Syllable& operator= ( Syllable&& ) = default;
 
    double t;
    wxString text;

src/Tags.h

@@ -74,7 +74,7 @@ class AUDACITY_DLL_API Tags final : public XMLTagHandler {
  public:
    Tags();  // constructor
    Tags( const Tags& ) = default;
-   Tags( Tags && ) {}
+   //Tags( Tags && ) = default;
    virtual ~Tags();
 
    std::shared_ptr<Tags> Duplicate() const;

src/effects/lv2/LV2Effect.h

@@ -63,8 +63,8 @@ public:
    }
    LV2Port( const LV2Port & ) = default;
    LV2Port& operator = ( const LV2Port & ) = default;
-   LV2Port( LV2Port && ) {}
-   LV2Port& operator = ( LV2Port && ) { return *this;}
+   //LV2Port( LV2Port && ) = default;
+   //LV2Port& operator = ( LV2Port && ) = default;
 
    uint32_t mIndex;
    wxString mSymbol;

src/effects/nyquist/Nyquist.h

@@ -49,8 +49,8 @@ public:
    NyqControl() = default;
    NyqControl( const NyqControl& ) = default;
    NyqControl &operator = ( const NyqControl & ) = default;
-   NyqControl( NyqControl && ) {}
-   NyqControl &operator = ( NyqControl && ) { return *this;}
+   //NyqControl( NyqControl && ) = default;
+   //NyqControl &operator = ( NyqControl && ) = default;
 
    int type;
    wxString var;

src/export/Export.h

@@ -41,8 +41,8 @@ class AUDACITY_DLL_API FormatInfo
       FormatInfo() {}
       FormatInfo( const FormatInfo & ) = default;
       FormatInfo &operator = ( const FormatInfo & ) = default;
-      FormatInfo( FormatInfo && ) {}
-      FormatInfo &operator = ( FormatInfo && ) { return *this;}
+      //FormatInfo( FormatInfo && ) = default;
+      //FormatInfo &operator = ( FormatInfo && ) = default;
       ~FormatInfo() {}
 
       wxString mFormat;

src/widgets/KeyView.h

@@ -33,8 +33,8 @@ public:
    }
    KeyNode( const KeyNode & ) = default;
    KeyNode &operator = ( const KeyNode & ) = default;
-   KeyNode( KeyNode && ) {}
-   KeyNode &operator = ( KeyNode && ) { return *this;}
+   //KeyNode( KeyNode && ) = default;
+   //KeyNode &operator = ( KeyNode && ) = default;
 
 public:
    wxString name;

src/widgets/NumericTextCtrl.cpp

@@ -239,8 +239,8 @@ public:
    }
    NumericField( const NumericField & ) = default;
    NumericField &operator = ( const NumericField & ) = default;
-   NumericField( NumericField && ) {}
-   NumericField &operator = ( NumericField && ) { return *this;}
+   //NumericField( NumericField && ) = default;
+   //NumericField &operator = ( NumericField && ) = default;
    void CreateDigitFormatStr()
    {
       if (range > 1)