Don't export template class.

The explicit instantiations are exported already.

src/Magnum/BufferImage.h

@@ -47,7 +47,7 @@ Stores image data in GPU memory. Interchangeable with @ref Image,
 @see @ref BufferImage1D, @ref BufferImage2D, @ref BufferImage3D, @ref Buffer
 @requires_gles30 Pixel buffer objects are not available in OpenGL ES 2.0.
 */
-template<UnsignedInt dimensions> class MAGNUM_EXPORT BufferImage: public AbstractImage {
+template<UnsignedInt dimensions> class BufferImage: public AbstractImage {
     public:
         const static UnsignedInt Dimensions = dimensions; /**< @brief %Image dimension count */