Remove warning related to imperative assignments (#8288)
Remove warning related to imperative assignments (#8288)

Closes #8285.

This warning has to be removed because all of the forms were
unified in v1.7, making case/with/if to behave the same.
That leads to undesired warnings in cases such as:

    a = 1

    with {:ok, a} <- my_fun(a) do
      :ok
    end
kelvinst/elixir,elixir-lang/elixir,kimshrier/elixir,michalmuskala/elixir,pedrosnk/elixir,ggcampinho/elixir,joshprice/elixir,lexmag/elixir,ggcampinho/elixir,pedrosnk/elixir,kimshrier/elixir,lexmag/elixir,kelvinst/elixir