Remove duplicate button to add new metrics

- Remove "new metrics" duplicated button and replace with a message
- Replace css with utility classes in the prometheus metrics view
- Remove unused css

app/assets/stylesheets/pages/settings.scss

@@ -272,7 +272,7 @@
   }
 
   .custom-monitored-metrics {
-    .card-title {
+    .card-header {
       display: flex;
       align-items: center;
 
@@ -292,17 +292,6 @@
     }
   }
 
-  .loading-metrics,
-  .empty-metrics {
-    padding: 30px 10px;
-
-    p,
-    .btn {
-      margin-top: 10px;
-      margin-bottom: 0;
-    }
-  }
-
   .loading-metrics .metrics-load-spinner {
     color: $gl-gray-700;
   }

app/views/projects/services/prometheus/_metrics.html.haml

@@ -8,15 +8,16 @@
 .col-lg-9
   .card.js-panel-monitored-metrics{ data: { active_metrics: active_common_project_prometheus_metrics_path(project, :json), metrics_help_path: help_page_path('user/project/integrations/prometheus_library/index') } }
     .card-header
+      %strong
         = s_('PrometheusService|Common metrics')
       %span.badge.badge-pill.js-monitored-count 0
     .card-body
       .loading-metrics.js-loading-metrics
-        %p.prepend-top-10.prepend-left-10
+        %p.m-3
           = icon('spinner spin', class: 'metrics-load-spinner')
           = s_('PrometheusService|Finding and configuring metrics...')
       .empty-metrics.hidden.js-empty-metrics
-        %p.text-tertiary.prepend-top-10.prepend-left-10
+        %p.text-tertiary.m-3
           = s_('PrometheusService|Waiting for your first deployment to an environment to find common metrics')
       %ul.list-unstyled.metrics-list.hidden.js-metrics-list