[llvm] [AMDGPU] Remove EXP_POS_ACCESS, EXP_PARAM_ACCESS. NFC. (PR #144361)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Actually the separate types might be required to account for the fact that different types of export do not necessarily complete in order with each other.

Confirmed. We should really have some proper tests for this, for all different export targets.

https://github.com/llvm/llvm-project/pull/144361