plugins.nrk: Fixed _id_re regex not matching series URLs.
plugins.nrk: Fixed _id_re regex not matching series URLs.

Also removed unused _program_id regex.

beardypig/streamlink,sbstp/streamlink,javiercantero/streamlink,sbstp/streamlink,fishscene/streamlink,ethanhlc/streamlink,gravyboat/streamlink,chhe/streamlink,streamlink/streamlink,fishscene/streamlink,back-to/streamlink,chhe/streamlink,bastimeyer/streamlink,javiercantero/streamlink,beardypig/streamlink,melmorabity/streamlink,gravyboat/streamlink,streamlink/streamlink,back-to/streamlink,melmorabity/streamlink,mmetak/streamlink,mmetak/streamlink,wlerin/streamlink,bastimeyer/streamlink,wlerin/streamlink,ethanhlc/streamlink