remove @staticmethod decorators

There might have been a time when calling a static method was faster
than a regular method, but that is no longer the case. According to
micro-benchmarks, it is 70% slower in CPython 3.13 and it also makes
executing the code of a class definition slower.

gallery_dl/extractor/flickr.py

@@ -585,8 +585,7 @@ class FlickrAPI(oauth.OAuth1API):
         if "license" in photo:
             photo["license_name"] = self.LICENSES.get(photo["license"])
 
-    @staticmethod
-    def _clean_info(info):
+    def _clean_info(self, info):
         info["title"] = info["title"]["_content"]
         info["description"] = info["description"]["_content"]
         return info