message: Don't fallback to IPU model
  Summary: Part of T7775
  Test Plan:
  all tests pass
  tensorflow_packaging has been updated too in D10374
  Reviewers: davidn, jakeh
  Maniphest Tasks: T7775
diff: @@ -592,7 +592,9 @@ Status PoplarExecutor::ConfigurePoplarDevice(const IpuOptions& cfg) {
  hardware_configured_ = true;
  }
  - if (getenv(s_force_ipu_model) == nullptr) {
  + const bool force_ipu_model = getenv(s_force_ipu_model) != nullptr;
  +
  + if (!force_ipu_model) {
  auto device_list = GetDeviceManager().getDevices();
  for (const auto& d : device_list) {
  if (d.getTarget().getTargetType() == poplar::TargetType::IPU) {
  @@ -669,7 +671,7 @@ Status PoplarExecutor::ConfigurePoplarDevice(const IpuOptions& cfg) {
  option_flags_.set("debug.executionProfile", "compute_sets");
  }
  }
  - } else {
  + } else if (force_ipu_model) {
  if (current_config_.ipu_model_config().enable_ipu_model()) {
  // Poplar IPU Model device
  