Don't delete "frequently visited projects" for each session

gitlab-ce~2278648

problem

The "frequently visited projects" are deleted every time a user logs in.

steps to reproduce

1. visit a few projects
2. log out
3. log in
4. on the dashboard bar > click on "projects"

current behavior

empty pop-up window

expected behavior

The frequently visited projects from previous sessions should be kept.
That's the whole point of "frequently visited projects".

output of checks

This bug happens on GitLab.com