After the launchscreen, but before app is loaded, there\'s a \"Loading from pre-bundled file\" message that appears at the top of the screen for just a few hundred milliseconds.
To disable the developer menu and therefore your mentioned message, you should change your Build Configuration to Release.
For iOS open your project in Xcode and select Product → Scheme → Edit Scheme... (or press ⌘ + <). Next, select Run from the menu on the left and change the Build Configuration to Release.