Remove all the CI configurations for the 'release' branch

The 'release' branch is now dead as we will switch to the new branching scheme.

Change-Id: I3254ee79e4513f254f347be13acc5bb7c551d4d2
Reviewed-by: Jani Heikkinen <jani.heikkinen@digia.com>
Reviewed-by: Simo Fält <simo.falt@digia.com>