docs: remove function call from all backend feature installation instructions

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

docs/backend-system/architecture/02-backends.md

@@ -24,7 +24,7 @@ const backend = createBackend();
 backend.add(import('@backstage/plugin-catalog-backend/alpha'));
 
 // Features can also be installed using an explicit reference
-backend.add(scaffolderPlugin());
+backend.add(scaffolderPlugin);
 
 // Start up the backend
 backend.start();

docs/backend-system/architecture/04-plugins.md

@@ -41,7 +41,7 @@ The `createBackendPlugin` return value is exported as `examplePlugin`, which is
 ```ts
 import { examplePlugin } from 'backstage-plugin-example-backend';
 
-backend.add(examplePlugin());
+backend.add(examplePlugin);
 ```
 
 By convention every plugin package should export its plugin instance as the default export from the package:

docs/backend-system/building-backends/08-migrating.md

@@ -675,7 +675,7 @@ backend.add(
   import('@backstage/plugin-catalog-backend-module-scaffolder-entity-model'),
 );
 /* highlight-add-next-line */
-backend.add(catalogModuleCustomExtensions());
+backend.add(catalogModuleCustomExtensions);
 ```
 
 This also requires that you have a dependency on the corresponding node package,
@@ -762,9 +762,9 @@ const otherPluginModuleCustomExtensions = createBackendModule({
 const backend = createBackend();
 backend.add(import('@backstage/plugin-events-backend/alpha'));
 /* highlight-add-next-line */
-backend.add(eventsModuleCustomExtensions());
+backend.add(eventsModuleCustomExtensions);
 /* highlight-add-next-line */
-backend.add(otherPluginModuleCustomExtensions());
+backend.add(otherPluginModuleCustomExtensions);
 ```
 
 Here we've placed the module directly in the backend index file just to get
@@ -841,7 +841,7 @@ const scaffolderModuleCustomExtensions = createBackendModule({
 const backend = createBackend();
 backend.add(import('@backstage/plugin-scaffolder-backend/alpha'));
 /* highlight-add-next-line */
-backend.add(scaffolderModuleCustomExtensions());
+backend.add(scaffolderModuleCustomExtensions);
 ```
 
 This also requires that you have a dependency on the corresponding node package,