[io grant] Fix up IO::Handle.print-nl

- The handle can be not for a file
- Remove all the prose about .nl-out's defaults and .opens.
    That's not the only way to set that attribute.

Author: zoffixznet

doc/Type/IO/Handle.pod6

@@ -309,14 +309,12 @@ Defined as:
 
     method print-nl(IO::Handle:D: --> True)
 
-Writes a newline to the filehandle. The newline marker, which is stored
-in the attribute C<$.nl-out>, defaults to C<\n> unless another marker has
-been specified in the call to L<open>.
+Writes the value of C<$.nl-out> attribute into the handle.
 
 =for code :skip-test
 my $fh = open 'path/to/file', :w, nl-out => "\r\n";
 $fh.print("some text");
-$fh.print-nl;                                        # \r\n
+$fh.print-nl; # prints \r\n
 $fh.close;
 
 =head2 method printf