Are you able to put the DB into full recovery model, set the server up for replication (you will need to add it from setup if it's not already present), create a publication in the problem DB, publish a table (any table) and then completely remove replication?
It's obviously stuck in a situation where it's a copy of a database that didn't have replication removed.
You might not even need to publish a table. Can you just try:
-- Enable distribution (which will need a distribution database) then do the following:
-- Enable replication for the DB
EXEC sp_replicationdboption @dbname = 'TheDatabase', @optname = N'publish', @value = N'true';
GO
-- Remove the publication
-- This command needs the name of the publication (Refresh in SSMS to check the name)
EXEC sp_removedbreplication 'SomePublication_TheDatabase','both';
GO
-- Disable replication for the DB
EXEC sp_replicationdboption @dbname = 'TheDatabase', @optname = N'publish', @value = N'false';
GO
-- Then remove replication/distribution