[1.16.X] Optifine sky textures reference non-existent files and are missing required properties

[MarkKoz]

Describe the Issue
The following source files are referenced but do not exist:

cloud2.png
sky_clouds1.png
sky_starfield.png
cloud2.png
cloud1.png
starfield02.png
sky_sunflare3.png
sky_clouds.png

sky14.properties is missing the following properties, which are documented as required:

startFadeIn
endFadeIn
endFadeOut

To Reproduce
Steps to reproduce the behavior:

1. Go to assets/minecraft/optifine/sky/world0/
2. Observe the listed files are missing from the directory.
3. Open each .properties file
4. Observe that some reference the listed files or are missing the required properties.

Expected Behavior
Referenced source files should not be missing and all required properties should be present.

Additional Context
I'm attempting to use MCPPPP to convert this resource pack's sky to the FabricSkyboxes format. It works according to spec; it's just that this resource pack is faulty.