ISSUE_TEMPLATE: delete tracking_issue template

As discussed in #368656.

Approved-by: Yohann Boniface <edhyjox@gmail.com>
Signed-off-by: Fernando Rodrigues <alpha@sigmasquadron.net>

.github/ISSUE_TEMPLATE/tracking_issue.md

@@ -1,39 +0,0 @@
----
-name: Tracking issue
-about: Provide an overview on a multi-step effort
-title: 'Tracking issue: ISSUENAME'
-labels: '5.scope: tracking'
-assignees: ''
-
----
-
-### Tracking description
-
-<!--
-Provide a brief summary of the project or multi-step effort. Explain why it is
-necessary and what the goals are.
-
-You may include way to reproduce the problem, screenshots or any information
-that you find relevant.
--->
-
-#### Reference Issue(s)/PR(s)
-
-- ...
-
-### Follow-up issues/notes
-
-<!--
-List any follow-up issues that need to be addressed after the main tasks are
-completed, or any notes related to the project.
--->
-
-#### Additional context
-Add any other context about the problem here.
-
----
-
-Add a :+1: [reaction] to [issues you find important].
-
-[reaction]: https://github.blog/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/
-[issues you find important]: https://github.com/NixOS/nixpkgs/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc