remove mention of PWP::Encoding

Hi,

I've removed unneeded mentions for PWP::Encoding plugin (see this dagolden/Dist-Zilla-PluginBundle-DAGOLDEN/pull/5 issue for details).

Feel free to comment on my quest as well:

> http://questhub.io/realm/perl/quest/5277f3cc9f567ad56f0000e7