Remove unused warning in pipeline graph

We had a computer prop `alert()` to decide which alert
to render based on some conditions. We had errors and warnings,
but we removed warnings and forgot to remove the unused property.
This removes the unused code.

app/assets/javascripts/pipelines/components/pipeline_graph/pipeline_graph.vue

@@ -64,13 +64,6 @@ export default {
     hasHighlightedJob() {
       return Boolean(this.highlightedJob);
     },
-    alert() {
-      if (this.hasError) {
-        return this.failure;
-      }
-
-      return this.warning;
-    },
     failure() {
       switch (this.failureType) {
         case DRAW_FAILURE:
@@ -210,11 +203,11 @@ export default {
   <div>
     <gl-alert
       v-if="hasError"
-      :variant="alert.variant"
-      :dismissible="alert.dismissible"
-      @dismiss="alert.dismissible ? resetFailure : null"
+      :variant="failure.variant"
+      :dismissible="failure.dismissible"
+      @dismiss="resetFailure"
     >
-      {{ alert.text }}
+      {{ failure.text }}
     </gl-alert>
     <div
       v-if="!hideGraph"