message: Remove reference to removed mlir_gpu prototype from docs.
diff: @@ -141,7 +141,7 @@ Conclusions:
  * ElementalIrEmitter ops go for (4), but not incrementally. There is no way to
  do it op by op, because all elementally-emitted ops are connected into the
  same graph. This work can also serve as a unification point of several
  - on-going forces (xla/service/mlir\_gpu, the kernel generator, Linalg).
  + on-going forces (the kernel generator, Linalg).
  * All other ops go for (1). As a stretch goal, they might be migrated to (3)
  or (4).
  