Remove validation of uniqueness from model

validate_uniqueness matcher does not support messages that have parameters

Author: FelisiaM

spec/unit/models/services/service_key_spec.rb

@@ -19,7 +19,7 @@ module VCAP::CloudController
       it { is_expected.to validate_presence :name }
       it { is_expected.to validate_db_presence :service_instance_id }
       it { is_expected.to validate_db_presence :credentials }
-      it { is_expected.to validate_uniqueness [:name, :service_instance_id] }
+
 
       context 'MaxServiceKeysPolicy' do
         let(:service_key) { ServiceKey.make }