google is one of the manufacturer meta tags we're cleaning up. Many of the posts with this tag have been migrated away (e.g., to Web Apps), and the tags then get changed to appropriate tags for the new site. However, the question originated here so it remains in the list of questions for the [google] tag (with a migrated indicator). We can't clean up the tag on these questions because it isn't actually here.
Does anyone know if the system is smart enough to recognize that these are phantom tags (in which case, the tag will automatically disappear when the only questions associated with it are migrated ones), or do we need to do something to manually purge the tag at that point?