Remove titles from security-links in sidebars

What does this MR do?

Both top-level navigation items that link to the projects' and the group's security dashboard contain title-attributes.

This is inconsistent with the rest of the navigation and this MR removes the title-attributes for both elements.

Related discussion: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14628#note_198398648

Before

After