chore: remove redundant 'bs.app' check

Author: shakyShane

lib/browser-sync.js

@@ -378,10 +378,6 @@ BrowserSync.prototype.serveFile = function (path, props) {
         route: path
     };
 
-    if (!bs.app) {
-        return;
-    }
-
     bs._addMiddlewareToStack(entry);
 };