message: Remove the use of dynamic output indices.
  As we now enable dynamic shaped hlos. We don't need to use an additional
  data structure to hold which outputs are dynamic.
diff: @@ -835,7 +835,6 @@ Status InsertSliceToDynamicBeforeModuleOutputs(
  }
  }
  });
  - int64 dynamic_index = 0;
  if (!dynamic_outputs.empty()) {
  if (root->shape().IsTuple()) {
  std::vector<HloInstruction*> new_root_operands;
  @@ -874,18 +873,8 @@ Status InsertSliceToDynamicBeforeModuleOutputs(
  }
  }
  // This is a dynamic output, add slice operation.
  - //
  - // Write the backend config in the format of
  - // 'dynamic_index'-'output_index'.
  - //
  - // dynamic_index indicates the position of this output in all dynamic
  - // outputs.
  - //
  - // output_index indicates the position of this output in all outputs
  - // (including static inputs).
  auto slice = HloInstruction::CreateCustomCall(
  - dynamic_subshape, slice_operands, "SliceToDynamic",
  - absl::StrFormat("%d-%d", dynamic_index++, index[0]));
  + dynamic_subshape, slice_operands, "SliceToDynamic");
  new_root_operands.push_back(
  module->entry_computation()->AddInstruction(std::move(slice)));
  } else {
  