iTunes 12.7, released 9/12/17, has removed all iOS app management features (that previously were available when an iOS device was connected to the Mac). This includes the iOS App Store, the ability to install/delete/backup iOS apps, and option for organizing iOS app placement on iOS screens.
This new iTunes 12.7 will show as an update for those running Mac OS 10.10.5 through 10.13, or to Windows users with iTunes installed.
The sudden removal of iTunes iOS app management has received harsh criticism, especially from the enterprise sector where iTunes is commonly used to install Volume Purchase Program iOS apps. A high number of posts from consumer users can also be found in the various online Apple support groups criticizing Apple for their decision to abandon iOS app management from workstations.
Update – 9/23/17
In response, Apple has posted a “stealth” version of iTunes 12.6.3 that retains these iOS app management features. It is available for download for Mac and PC, and after install the option for updating to iTunes 12.7 will no longer show. It can also be installed on top of iTunes 12.7.
The reason I call this a “stealth” version is that Apple has stated they won’t support it, nor will it be updated in the future. It is a short-term solution to appease people that were caught off guard by this change.