Remove a section for a now fixed bug

Those guidelines where based on
https://gitlab.com/gitlab-org/gitlab-docs/issues/311 which seems
to be fixed.

doc/development/documentation/styleguide.md

@@ -506,15 +506,6 @@ Example:
 For more information, see the [confidential issue](../../user/project/issues/confidential_issues.md) `https://gitlab.com/gitlab-org/gitlab-ce/issues/<issue_number>`.
 ```
 
-### Unlinking emails
-
-By default, all email addresses will render in an email tag on docs.gitlab.com.
-To escape the code block and unlink email addresses, use two backticks:
-
-```md
-`` example@email.com ``
-```
-
 ## Navigation
 
 To indicate the steps of navigation through the UI: