Removed workaround for intermittent ghost-server logging

- upon further testing, this started to not work again so I'm removing
  this horrible hack
- it could be Bunyan playing around with us, and the server is actually
  shutting down

core/server/ghost-server.js

@@ -169,9 +169,6 @@ class GhostServer {
             this.httpServer = null;
             this._logStopMessages();
         }
-
-        // TODO: investigate why this is required (see commit)
-        return Promise.resolve();
     }
 
     /**
@@ -206,9 +203,6 @@ class GhostServer {
         // Wait for all cleanup tasks to finish
         await Promise
             .all(this.cleanupTasks.map(task => task()));
-
-        // TODO: investigate why this is required (see commit)
-        return Promise.resolve();
     }
 
     _onShutdownComplete() {