Well, you mentioned much; yet, managed to not include the actual 'GNU/GPL Workflow' file's / installer's name and its related web page.
Since no specific automator workflow name was provided, one can only make some assumptions, and provide a vague response.
Locate your '~/Library/Automator/' folder. 'Tiger' only installs 'Create Preview and Icon.action', 'Remove Resourcefork.action', 'Convert into JPEG.action', and 'Rotate JPEG Lossless.action'. Your (unknown named) 'GNU/GPL Workflow' most likely added a '.action' file here; find and trash it.
Next, a folder titled 'Workflows' was created in the '/Library/' folder (if it did not already exist). Within the 'Workflows' folder a series of folders may have been created, and finally a file or files placed into the '/Library/Applications/Finder/' folder. Navigate to the 'Workflows' 'Finder' folder and remove any files installed by the (unknown name) 'GNU/GPL Workflow' installer.
By launching 'Automator' you should be able to verify that the (unknown name) 'GPU/GPL Workflow' is no longer listed under 'Finder's 'Actions' column.