SceneGraph: use protected destructor rather than pure virtual one.

The Transformation classes are always instantiated by inheritance, thus
we don't need any virtual deletion capabilities.

src/SceneGraph/AbstractTransformation.h

@@ -62,7 +62,6 @@ template<UnsignedInt dimensions, class T> class MAGNUM_SCENEGRAPH_EXPORT Abstrac
         static const UnsignedInt Dimensions = dimensions;
 
         explicit AbstractBasicTransformation();
-        virtual ~AbstractBasicTransformation() = 0;
 
         #ifdef DOXYGEN_GENERATING_OUTPUT
         /**
@@ -143,6 +142,9 @@ template<UnsignedInt dimensions, class T> class MAGNUM_SCENEGRAPH_EXPORT Abstrac
             return this;
         }
 
+    protected:
+        ~AbstractBasicTransformation() = default;
+
     #ifdef DOXYGEN_GENERATING_OUTPUT
     protected:
     #else

src/SceneGraph/AbstractTranslationRotation2D.h

@@ -73,6 +73,9 @@ template<class T> class AbstractBasicTranslationRotation2D: public AbstractBasic
         }
         #endif
 
+    protected:
+        ~AbstractBasicTranslationRotation2D() = default;
+
     #ifdef DOXYGEN_GENERATING_OUTPUT
     protected:
     #else

src/SceneGraph/AbstractTranslationRotation3D.h

@@ -120,6 +120,9 @@ template<class T> class AbstractBasicTranslationRotation3D: public AbstractBasic
         }
         #endif
 
+    protected:
+        ~AbstractBasicTranslationRotation3D() = default;
+
     #ifdef DOXYGEN_GENERATING_OUTPUT
     protected:
     #else

src/SceneGraph/AbstractTranslationRotationScaling2D.h

@@ -70,6 +70,9 @@ template<class T> class AbstractBasicTranslationRotationScaling2D: public Abstra
         }
         #endif
 
+    protected:
+        ~AbstractBasicTranslationRotationScaling2D() = default;
+
     #ifdef DOXYGEN_GENERATING_OUTPUT
     protected:
     #else

src/SceneGraph/AbstractTranslationRotationScaling3D.h

@@ -82,6 +82,9 @@ template<class T> class AbstractBasicTranslationRotationScaling3D: public Abstra
         }
         #endif
 
+    protected:
+        ~AbstractBasicTranslationRotationScaling3D() = default;
+
     #ifdef DOXYGEN_GENERATING_OUTPUT
     protected:
     #else

src/SceneGraph/Object.hpp

@@ -42,7 +42,6 @@ template<UnsignedInt dimensions, class T> AbstractBasicObject<dimensions, T>::Ab
 template<UnsignedInt dimensions, class T> AbstractBasicObject<dimensions, T>::~AbstractBasicObject() {}
 
 template<UnsignedInt dimensions, class T> AbstractBasicTransformation<dimensions, T>::AbstractBasicTransformation() {}
-template<UnsignedInt dimensions, class T> AbstractBasicTransformation<dimensions, T>::~AbstractBasicTransformation() {}
 
 template<class Transformation> Object<Transformation>::~Object() = default;