We often run into this in our QA environments. The below script is a blunt hammer approach to remove replication, no matter how fubared your server is:

USE <yourreplicateddb>

EXEC sp_removedbreplication...

I'm creating scripts for deployment, so it was simpler to use xp_regwrite:

EXEC master..xp_regwrite

@rootkey='HKEY_LOCAL_MACHINE',

@key='SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\SQLServerAgent',

...