simplify skipped links deduplication

Author: ronaudinho

src/pip/_internal/index/package_finder.py

@@ -696,11 +696,9 @@ def set_prefer_binary(self):
 
     def skipped_links_requires_python(self):
         # type: () -> List[str]
-        skips = [skip[1] for skip in self._logged_links if 'Requires-Python' in skip[1]]
-        # cleans duplicate package version found from different links
-        skips = list(dict.fromkeys(skips))
-        skips.sort()
-        return skips
+        return sorted(
+            {reason for _, reason in self._logged_links if 'Requires-Python' in reason}
+        )
 
     def make_link_evaluator(self, project_name):
         # type: (str) -> LinkEvaluator