take PWP::Encoding away

Hi,

Pod::Weaver now [has *SingleEncoding* plugin as a part of *@Default* bundle (starting from 4.000)](http://rjbs.manxome.org/rubric/entry/2021), which makes Pod::Weaver::Plugin::Encoding an extra dependency that could be thrown away.

See my quest for details/comments:

> http://questhub.io/realm/perl/quest/5277f3cc9f567ad56f0000e7

Cheers,
Sergey