Unused File Group

Each database can have one or more File Groups, each with one or more files in them. Each database object (tables, indexes) is assigned to a file group. If a filegroup doesn't have any objects assigned to it, the files in that filegroup won't be used.

Suggested Action

Remove the filegroup and any associated data files.

1. How to Drop Empty Filegroup Data Files

REMOVE FILE ExtraDataFile;  

2. How to Remove Unused Filegroup From the Database

ALTER DATABASE [WhippetWorks]  
REMOVE FILEGROUP ExtraFilegroup;  

Further Reading

Remove Defunct Filegroups (SQL Server) | Microsoft Docs

ALTER DATABASE (Transact-SQL) File and Filegroup Options | Microsoft Docs