message: Support more control flow ops. Delete ops that require ref inputs (e.g.
  variables); these ops are not applicable to layout optimizer, because
  layout-agnostic nodes are never directly connected to variables, but to
  other layout-sensitive nodes such as conv and pooling.
diff: @@ -103,9 +103,11 @@ std::set<string> GetOpsFormatAgnostic() {
  "Div",
  "Elu",
  "EluGrad",
  + "Enter",
  "Equal",
  "Erf",
  "Erfc",
  + "Exit",
  "Exp",
  "Expm1",
  "Floor",
  @@ -138,6 +140,7 @@ std::set<string> GetOpsFormatAgnostic() {
  "Mod",
  "Mul",
  "Neg",
  + "NextIteration",
  "NotEqual",
  "OnesLike",
  "Pad",
  @@ -148,7 +151,6 @@ std::set<string> GetOpsFormatAgnostic() {
  "RealDiv",
  "Reciprocal",
  "ReciprocalGrad",
  - "RefIdentity",
  "Relu",
  "Relu6",
  "Relu6Grad",
  @@ -172,8 +174,6 @@ std::set<string> GetOpsFormatAgnostic() {
  "Switch",
  "TruncateDiv",
  "TruncateMod",
  - "RefMerge",
  - "RefSwitch",
  "Round",
  "Rsqrt",
  "RsqrtGrad",
  