Remove libultra functions from LUS.

[briaguya-ai]

Remove all of the libultra headers, and remove the implementations. libultra implementations will be the responsibility of the port.

We will want to create a new repository to host all of the implementations from current LUS, Kirito's SM64/SF64 fork, and the PD fork.

comment out all of gbi.h, uncomment until LUS builds, clean up, PR
remove all of libultra directory in LUS, add stuff back until it builds

[briaguya-ai]

did discovery here #410

removing most things went smoothly, but gfx_pc is heavily coupled to gbi. it's a bit of a tangled mess and it seems like the only real way to separate that would be a full refactor - i don't see a quick way to take a partial step in the right direction.