Undo eta expansion for parameterless and nullary methods
Transform a function node (x_1,.
Transform a function node (x_1,...,x_n) => body of type FunctionN[T_1, .., T_N, R] to
class $anon() extends AbstractFunctionN[T_1, .., T_N, R] with Serializable { def apply(x_1: T_1, ..., x_N: T_n): R = body } new $anon()