Delete gGfxSPTaskOutputBufferSize if possible

[MegaMech]

This probably requires GCC PR merged first.

But thus far it seems the bufferSize variable isn't really necessary. Should be able to do like an ARRAY_COUNT() macro or similar.

However, when it gets removed everything gets shifted. And it might be weird having a GFX_OUTPUT_BUFFER_SIZE of 0x3f01
That doesn't work of course because the output buffer is a u64 so that actually makes it too big.