is_struct/1 fixes (#9481)
is_struct/1 fixes (#9481)

* Remove duplicate test

* Simplify name of private function in is_struct/1 test script

michalmuskala/elixir,kimshrier/elixir,pedrosnk/elixir,kelvinst/elixir,pedrosnk/elixir,kimshrier/elixir,elixir-lang/elixir,ggcampinho/elixir,joshprice/elixir,kelvinst/elixir,ggcampinho/elixir