docs: remove flatshading update info

Author: sciecode

docs/manual/en/introduction/How-to-update-things.html

@@ -178,8 +178,6 @@ <h2>Materials</h2>
 
 			<p>Also GLstate related parameters can change any time (depthTest, blending, polygonOffset, etc).</p>
 
-			<p>Flat / smooth shading is baked into normals. You need to reset normals buffer (see above).</p>
-
 			<p>The following properties can't be easily changed at runtime (once the material is rendered at least once):</p>
 			<ul>
 				<li>numbers and types of uniforms</li>