refactor!: 🔥 remove deprecated image effect implementation (#23)

The image effect component implementation is very cumbersome and error prone. Support from Unity for this old implementation is lacking as well. Hence I don't want to support it anymore.

Removes image effect component. For use with the built-in pipeline use the post-processing implementation instead.

README.md

@@ -27,7 +27,6 @@ If in doubt try to import the sample you want to use and start from there.
    - **High-Definition Render Pipeline:** Create a [Custom Pass volume](https://docs.unity3d.com/Packages/com.unity.render-pipelines.high-definition@12.1/manual/Custom-Pass-Creating.html) and add `OitRenderPass` to it.
    - **Universal Render Pipeline:** Add the renderer feature `Order Independent Transparency Renderer` to your Universal Renderer Asset. _Note: URP documentation only describes a [fullscreen Blit](https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@15.0/manual/renderer-features/how-to-fullscreen-blit.html) which only works in Game view. If you know whether a fullscreen Blit in URP in Scene view as well as in Game view is possible, help would be very much appreciated._
    - **Post-Processing Stack v2:** Add the post-processing override `Order Independent Transparency` to a post-processing volume in your scene.
-   - **ImageEffect Component:** Add the component `OitImageEffectComponent` to your scene e.g. to your main camera.
 
 2. Change the material of every object that shall be rendered with order-independent transparency. They have to be rendered with a shader writing to the buffer used by the order-independent transparency implementation. Two sample shaders that you can use are included in this project: `OrderIndependentTransparency/Unlit` for all pipelines and additionally `OrderIndependentTransparency/Standard` for the built-in pipeline.