* As per code reviews (see T54721 and T54769), it was decided that the "VFX Modifiers" should not be in the modifiers stack, as they are not really modifiers. Instead, they are more like placeholders for shader effects on the object. For now, we simply remove these from the code, with a view towards designing a more general solution for all object types in 2.8 in future (e.g. as a "Viewport Effects" tab or similar in the Properties Editor)
* Also removed the "DOF" code. This was trying to copy what was done for Eevee, but the results were low quality, and the relevant code paths were already commented out. This code is also removed in this commit, as it depended a lot on many of the things put in place for the VFX modifiers, making removal of the VFX buffers complicated. Since it's not used now, it's not a big loss. Besides, with version control, we can bring this back in future.
NOTE: Blender still doesn't compile - there are still too many extra buffers hanging around that need to be removed