cleanup: How-to-use-post-processing.html (#28168)

Improved Output Pass related statement.

Since the tone mapping is being extracted from the renderer state, the term 'optional' seems to be a bit misleading / outdated ( as per the changes mentioned in https://github.com/mrdoob/three.js/wiki/Migration-Guide#154--155 )

docs/manual/en/introduction/How-to-use-post-processing.html

@@ -77,7 +77,7 @@
 
 		<p>
 			`RenderPass` is normally placed at the beginning of the chain in order to provide the rendered scene as an input for the next post-processing step. In our case,
-			`GlitchPass` is going to use these image data to apply a wild glitch effect. `OutputPass` is usually the last pass in the chain which performs sRGB color space conversion and optional tone mapping.
+			`GlitchPass` is going to use these image data to apply a wild glitch effect. `OutputPass` is usually the last pass in the chain which performs sRGB color space conversion and tone mapping.
 			Check out this [link:https://threejs.org/examples/webgl_postprocessing_glitch live example] to see it in action.
 		</p>