Remove unused headers.

code/ObjFileImporter.cpp

@@ -47,10 +47,10 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "ObjFileData.h"
 #include "IOStreamBuffer.h"
 #include <memory>
-#include <assimp/Importer.hpp>
 #include <assimp/scene.h>
 #include <assimp/ai_assert.h>
 #include <assimp/DefaultLogger.hpp>
+#include <assimp/importerdesc.h>
 
 static const aiImporterDesc desc = {
     "Wavefront Object Importer",