This PR intends to remove XLA as a bzlmod and transfer it as a non
bzlmod dep.
This is because this module will never be upstreamed as is, so keep it
private.
Also, we fetch llvm-raw and stablehlo from it, which is fine.
While there, dummify the various local_config XLA symbols to please the
imports, as we don't use those parts in ZML itself.
Closes
