emit event when removing OAuth2Client record

app/services/oauth2.js

@@ -464,6 +464,10 @@ class OAuth2Service extends SiteService {
    * @param {OAuth2Client} client the client to be removed
    */
   async removeClient (client) {
+    // provides opportunity to allow or disallow and, if allowed, perform any
+    // additional cleanup needed when removing a client.
+    await this.emitDtpEvent('client.remove', client);
+
     this.log.info('removing client', { clientId: client._id, });
     await OAuth2Client.deleteOne({ _id: client._id });
   }