Zombie Sql Server DB on Secondary Replica is both in and out of an Availability Group
I pulled the oldest full backup I could find and was able to restore that over the Restoring db using:

RESTORE DATABASE [ZOMBIEDB] FROM  DISK = N'D:\ZOMBIEDB.bak' WITH  FILE = 1,  NOUNLOAD,  REPLACE,  STATS = 5


I was then able to delete the restored database.