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/wikimedia.py

@@ -52,8 +52,7 @@ class WikimediaExtractor(BaseExtractor):
                 return url
         raise exception.StopExtraction("Unable to find API endpoint")
 
-    @staticmethod
-    def prepare(image):
+    def prepare(self, image):
         """Adjust the content of an image object"""
         image["metadata"] = {
             m["name"]: m["value"]