Ref #3903 - Normalize methods listings

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3+
| Fixed tickets | #3903 

I only did this on methods listings which have some informations about the methods. (ie. I didn't change anything on this page: http://symfony.com/doc/current/contributing/code/conventions.html#method-names)
Can you reduce them to one blank line?