Can iOS apps be removed from iTunes Music Folder after upgrading to iTunes 12.7?
The short answer is: YES you can delete the folder.

The longer answer is: It depends on which apps you have. If you have some apps that you no longer can download from the App Store, you still need them as a backup, so that you can drop them onto your device when/if needed. So you can delete the apps that you know you still can update/download from the App Store.

And when you decide if you still need the old app, you should also see at the app’s spec. - is it a 32-bit or a 64-bit app ?? only 64-bit will work with iOS 11