Improve CI texture image support

[LucretiaArc]

The current CI texture image implementation has two issues:

• Additional Python packages are required
• Only the RGBA16 texel format is supported

Fast-64/fast64#719 adds an option to export CI texture images with texel format information in the file name, and n64graphics already supported CI textures, so this PR solves both problems at once.

Also:

• Removed the guard in n64graphics against CI word swapped textures.
• Removed n64graphics_ci, which wasn't used anywhere. It does support palette reduction using exoquant, which can't be said of the n64graphics implementation, so that might be worth implementing for n64graphics in future.

[gheskett]

Wait n64graphics already supported CI this entire time? What on earth was that script for lol

[arthurtilly]

i always used binpng for ci textures. okay but literally who has ever used a non-rgba16 ci texture is that a thing

[gheskett]

ia16 apparently 🤷

[arthurtilly]

who has ever used ia16 ever

[gheskett]

People that like transparent gradients I guess

[arthurtilly]

ia8 has 4 bit alpha

[gheskett]

Yeah but 4 bits of not alpha isn't very smooth

[arthurtilly]

still, i cant think of any situation where you wouldnt either wanna multitex with rgba or could just use i8