remove pod6 from supported list

Author: kivikakk

README.md

@@ -29,8 +29,6 @@ you wish to run the library. You can also run `script/bootstrap` to fetch them a
 * [.asciidoc, .adoc, .asc](http://asciidoc.org/) -- `gem install asciidoctor` (http://asciidoctor.org)
 * [.pod](http://search.cpan.org/dist/perl/pod/perlpod.pod) -- `Pod::Simple::XHTML`
   comes with Perl >= 5.10. Lower versions should install Pod::Simple from CPAN.
-* [.pod6](https://docs.perl6.org/language/pod) -- No additional
-  dependency beyond perl6 `Pod::To::HTML` (in stdlib)
 
 Installation
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