Remove invalid URL that make twine fail with error 400

Author: Pierre-Sassoulas

setup.cfg

@@ -30,7 +30,6 @@ keywords = static code analysis,python,abstract syntax tree
 project_urls =
     "Bug tracker" = https://github.com/PyCQA/astroid/issues
     "Discord server" = https://discord.gg/kFebW799
-    "Mailing list" = mailto:[email protected]
 
 [options]
 packages = find: