stow_node: remove comments about implementation details from POD

These don't add much value, and the reference to $source was out of
date anyway.

lib/Stow.pm.in

@@ -484,8 +484,6 @@ Relative path to symlink source from the dir of target.
 =back
 
 C<stow_node()> and C<stow_contents()> are mutually recursive.
-C<$source> and C<$target_subpath> are used for creating the symlink.
-C<$target_subpath> is used for folding/unfolding trees as necessary.
 
 =cut