Fix deselecting calendar days on contribution graph

## What does this MR do?
Fix deselecting calendar days on contribution graph

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
In `master`, you can currently deselect a calendar day after selecting but you cannot reselect that day.

## Screenshots (if relevant)
Before:
![2016-10-25_10.42.20](/uploads/7d442c09cd15082cf69f673a544b56f9/2016-10-25_10.42.20.gif)

After:
![2016-10-25_10.40.35](/uploads/6123365f0ec63ee84658ee6057e7715c/2016-10-25_10.40.35.gif)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #22381

See merge request !6453