Remove deploy_env from metrics cert generation
Remove deploy_env from metrics cert generation

Story #115318745 removed the need to concatenate the DEPLOY_ENV
variable and the system_dns_zone_name variable. However, the
DEPLOY_ENV variable was not removed from the metrics certificate
Common Name.

alphagov/paas-cf,jimconner/paas-cf,jimconner/paas-cf,jimconner/paas-cf,alphagov/paas-cf,alphagov/paas-cf,jimconner/paas-cf,jimconner/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,jimconner/paas-cf,alphagov/paas-cf,jimconner/paas-cf