Stop ignoring colored knife output config on Windows

We already set the correct default config of no color for knife on Windows at https://github.com/opscode/chef/blob/master/lib/chef/application/knife.rb#L48. So we should remove this override which causes us to ignore the config -- users with reasonable terminals like ConEmu can safely handle ANSI escape sequences for colored output, and we should let those users override the default config to allow for color rather than saying "you can't have color because you're on Windows."
@btm, @randomcamel, @jdmundrawala, thoughts?