cmd/prometheus: remove tests for old flags
cmd/prometheus: remove tests for old flags

kangwoo/prometheus,Conorbro/prometheus,Stackdriver/stackdriver-prometheus,AlekSi/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,Conorbro/prometheus,alileza/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,amorken/prometheus,Conorbro/prometheus,prometheus/prometheus,Stackdriver/stackdriver-prometheus,keegancsmith/prometheus,Conorbro/prometheus,brancz/prometheus,alileza/prometheus,brancz/prometheus,prometheus/prometheus,prometheus/prometheus,kangwoo/prometheus,amorken/prometheus,yanghongkjxy/prometheus,yanghongkjxy/prometheus,brancz/prometheus,keegancsmith/prometheus,amorken/prometheus,Gouthamve/prometheus,brancz/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,alileza/prometheus,AlekSi/prometheus,Stackdriver/stackdriver-prometheus,keegancsmith/prometheus,amorken/prometheus,Gouthamve/prometheus,GoogleCloudPlatform/prometheus,AlekSi/prometheus,yanghongkjxy/prometheus,alileza/prometheus,yanghongkjxy/prometheus,Gouthamve/prometheus,kangwoo/prometheus,Gouthamve/prometheus,AlekSi/prometheus,keegancsmith/prometheus,prometheus/prometheus