ConfirmRelease: remove obsolete code (EUMM loading) and doc

ExtUtils::MakeMaker::prompt is not used anymore for the prompt. So we
don't need to load EUMM anymore. One more speed up!
Thanks Devel::NYTProf for the catch!
Load Archive::Tar only when used (in Dist::Builder, Plugin::TestRelease)

Replace 'use Archive::Tar' with appropriate 'require Archive::Tar'.
One less module loaded every time.
Thanks to Devel::TraceUse for the catch.