Project:Ruby/Ruby 2.1 deprecation

Upstream support for Ruby 2.1 has ended on 31st March 2017.

Deprecation plan

 * Get ruby22 package coverage up to the same level as ruby21
 * Stabilize packages with ruby22 support
 * Default Ruby target for new installs to ruby22
 * Package.mask and remove ruby21-only packages

For further information please also check https://bugs.gentoo.org/show_bug.cgi?id=615822