Remove ISSUE_TEMPLATE as we're closing issues at github

.github/ISSUE_TEMPLATE.md

@@ -1,51 +0,0 @@
-<!--
-
-Thank you very much for contributing to imag.
-
-Please notice: I, the author of imag, am currently on a sabatical (May 2018
-until early 2019). I am not sure whether I will have access to the internet
-during that time. I may respond slowly - delay of 2-4 weeks or even more are
-possible! I hope it won't be more.
-
-
-For below: Omit the not applicable sections.
-
--->
-
-<!--
-
-IMPORTANT NOTICE
-
-We will close issue and PR contributions via github at some time in the future
-(more information [here](https://imag-pim.org/blog/2018/06/10/off-of-github/))!
-
-Github is only used for CI right now, main development continues on the
-mailinglist.
-
-Please send issues and pull requests (either via `git request-pull` or `git
-format-patch` + `git send-email`) to
-[the imag mailinglist](https://imag-pim.org/mailinglist/).
-
--->
-
-### Issue type
-
-- [ ] Bug
-- [ ] Idea/Feature request
-- [ ] Question/Other
-
-<!-- In case of a bug: -->
-
-### What I tried to do
-
-### What I expected to happen
-
-### What happened
-
-### My idea on how to solve this issue
-
-### Metadata
-
-* Output of `imag-<tool> --version`
-* Output of `imag --versions` (if multiple imag tools were used)
-