Scene: remove redundant pragma once statement.

include/assimp/scene.h

@@ -38,7 +38,6 @@ THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ---------------------------------------------------------------------------
 */
-#pragma once
 
 /** @file scene.h
  *  @brief Defines the data structures in which the imported scene is returned.