remove camera operation

I don't see why our export function should affect the camera.
I removed it here because camera is an empty list in the test.

brainrender/render.py

@@ -305,7 +305,6 @@ def export(self, savepath):
         plt = Plotter()
         plt.add(self.clean_renderables).render()
         plt = plt.show(interactive=False)
-        plt.camera[-2] = -1
 
         with open(path, "w") as fp:
             fp.write(plt.get_snapshot())