Revert "Add a static assertions for custom Op<> to not defined data m…

…embers (NFC)"

This reverts commit c0edcec.

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mlir/include/mlir/IR/OpDefinition.h

@@ -1780,8 +1780,6 @@ class Op : public OpState, public Traits<ConcreteType>... {
     return &verifyInvariants;
   }
   static LogicalResult verifyInvariants(Operation *op) {
-    static_assert(sizeof(ConcreteType) == sizeof(OpState),
-                  "Op class aren't allowed to have data members");
     return failure(
         failed(op_definition_impl::verifyTraits<VerifiableTraitsTupleT>(op)) ||
         failed(cast<ConcreteType>(op).verify()));