tools: remove readability/fn_size rule

PR-URL: https://github.com/nodejs/node/pull/54663
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

tools/cpplint.py

@@ -325,7 +325,6 @@ _ERROR_CATEGORIES = [
     'readability/casting',
     'readability/check',
     'readability/constructors',
-    'readability/fn_size',
     'readability/inheritance',
     'readability/pointer_notation',
     'readability/multiline_comment',