Linter: update to eslint v9

This eslint version brings breaking changes related to the eslint config.
eslint-airbnb-config has yet to release a compatible version with the
new format, and it generally looks unmaintained, hence we drop the dependency
in favor of the built-in recommended configs.

test/security/unsigned_subpackets.js

@@ -61,7 +61,7 @@ async function makeKeyValid() {
         encryptionKeys: k
       });
       return false;
-    } catch (e) {
+    } catch {
       return true;
     }
   }