Deprecate useless plugin export.

Signed-off-by: Eric Peterson <i.am@eric.pe>

plugins/analytics-module-ga/api-report.md

@@ -9,7 +9,7 @@ import { BackstagePlugin } from '@backstage/core-plugin-api';
 import { Config } from '@backstage/config';
 import { IdentityApi } from '@backstage/core-plugin-api';
 
-// @public (undocumented)
+// @public @deprecated (undocumented)
 export const analyticsModuleGA: BackstagePlugin<{}, {}>;
 
 // @public

plugins/analytics-module-ga/src/plugin.ts

@@ -16,6 +16,9 @@
 import { createPlugin } from '@backstage/core-plugin-api';
 
 /**
+ * @deprecated Importing and including this plugin in an app has no effect.
+ * This will be removed in a future release.
+ *
  * @public
  */
 export const analyticsModuleGA = createPlugin({