What Catholic saint lost his title of saint?

No saint has really lost their saint title. Several saints have been removed from the official calendar of saints because we lack evidence that they really existed and may have been fictional characters rather than actual people. Some examples:

St. Christopher

St. Barbara of Nicomedia

St. Dorothy

St. Philomena

St. Olivia

Some people have been removed from the calendar and then placed back on it when additional information or evidence is found. An example would be St. Catherine of Alexandria.