make sure that the stale header removal works the first time around

make sure that the stale header removal works the first time around

sort backwards by ascii, so that the lowercase headers come first -
otherwise the camelcase headers would survive the first round, as they
include the lowercase forwarding headers which were not deleted yet.

Change-Id: Iece2788206d31a11428f38da8d8f9f4d0b6dc992
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>