message: Use the GCL API
  Summary:
  Remove the old popops collective API
  Ref T16509
  Test Plan: All tests pass
  Reviewers: hakons, #tensorflow, #framework_ip_review_-_any_oss_or_third-party_code_use_has_been_approved, jakeh
  Maniphest Tasks: T16509
diff: @@ -300,8 +300,8 @@ class HostEmbeddingLookupOp : public PoplarOpDef {
  // Exchange the columns from this replica back to their respective replicas.
  // We also recieve the columns we requested from the other replicas.
  - host_sliceable.tensor = popops::allToAllPersonalizedExchange(
  - graph, host_sliceable.tensor, seq,
  + host_sliceable.tensor =
  + gcl::allToAll(graph, host_sliceable.tensor, seq,
  GetDebugName(inst) + "/exchange_columns",
  GetReplicatedCollectiveOptions(res));
  @@ -557,8 +557,8 @@ class HostEmbeddingUpdateOp : public PoplarOpDef {
  grads = grads.dimShuffle({1, 0, 2});
  // All-To-All exchange the grad columns with their respective replicas.
  - grads = popops::allToAllPersonalizedExchange(
  - graph, grads, seq, GetDebugName(inst) + "/exchange_columns",
  + grads = gcl::allToAll(graph, grads, seq,
  + GetDebugName(inst) + "/exchange_columns",
  GetReplicatedCollectiveOptions(res));
  grads = grads.flatten(0, 2);
  