Remove extra newline in top-level FunDef's string representation

[HertzDevil]

Removes the following empty line, which is always there for top-level funs:

{% p @top_level.methods.select(&.name.== "main")[0] %}

fun main(argc : Int32, argv : ::Pointer(::Pointer(UInt8))) : Int32
  Crystal.main(argc, argv)

end