angular-material: Revert deletion of hide css class

Revert the deletion of the hide css class in the angular material master detail renderer.
With this, the delete button is displayed only when an item is hovered and hidden.

Fixes #2327

packages/angular-material/src/library/other/master-detail/master.ts

@@ -144,6 +144,9 @@ export const removeSchemaKeywords = (path: string) => {
         top: 0;
         right: 0;
       }
+      .hide {
+        display: none;
+      }
       .show {
         display: inline-block;
       }