files_dir: remove trailing "research paper" in prep

Author: Gerit Wagner

colrev/packages/files_dir/src/files_dir.py

@@ -839,6 +839,7 @@ def _fix_special_outlets(self, *, record: colrev.record.record.Record) -> None:
             for suffix in [
                 "completed research paper",
                 "completed research",
+                "research paper",
                 "complete research",
                 "full research paper",
                 "research in progress",