This is a project without a workspace?
Close Xcode. Back up the .xcodeproj, then right click the original and Show Package Contents. Inisde, you’ll see a file called project.xcworkspace. This is a workspace created by Xcode when a project is open without a xcworkspace, and it contains this grouping information.
Move this to the trash and reopen the project in Xcode; it will generate a new, default project.xcworkspace without the grouping.