[ImportVerilog] Skip defparams which have been handled by slang.

[hailongSun2000]

For defparam, slang has propagated its value for the corresponding parameter. Such as:

module Top;
  Foo #(1) foo();
endmodule

module Foo #(
  parameter P = 32
);
  int a = P;
endmodule

module Bar;
  defparam Top.foo.P  = 4;
endmodule

On the AST, P and a both are 4. So we can skip defparam.

[fabianschuiki]

Nice 🥳!