extract `delete_cookie_header!` to a non-mutation based implementation
extract `delete_cookie_header!` to a non-mutation based implementation

this way we can manipulate cookies without depending on the cookies
being stored in a hash.

gioele/rack,shaneog/rack,liamseanbrady/rack,keepcosmos/rack,nmk/rack,davidcelis/rack,imtayadeway/rack,shaneog/rack,eins78/rack,wildjcrt/rack,rwz/rack,wildjcrt/rack,gfvcastro/rack,Eric-Guo/rack,eins78/rack,deepj/rack,ngpestelos/rack,jackxxu/rack,laplaceliu/rack,eins78/rack,maclover7/rack,wildjcrt/rack,Eric-Guo/rack,gfvcastro/rack,tylergannon/rack,tylergannon/rack,tylergannon/rack,keepcosmos/rack,davydovanton/rack,davydovanton/rack,imtayadeway/rack,imtayadeway/rack,maclover7/rack,liamseanbrady/rack,deepj/rack,jackxxu/rack,gioele/rack,keepcosmos/rack,laplaceliu/rack,supzann3/rack,gfvcastro/rack,ngpestelos/rack,nmk/rack,supzann3/rack,laplaceliu/rack,davidcelis/rack,akihiro17/rack,ngpestelos/rack,rwz/rack,supzann3/rack,wjordan/rack,wjordan/rack,davydovanton/rack,nmk/rack,liamseanbrady/rack,jackxxu/rack,davidcelis/rack,rwz/rack,deepj/rack,wjordan/rack,maclover7/rack,shaneog/rack,Eric-Guo/rack,akihiro17/rack,akihiro17/rack,gioele/rack