[fix] remove .github/ISSUE_TEMPLATE/discuss.md
In 2021 we did not used github-discussions, see commit message of 272c9d6b.
Theses days we use github-discussions and have a Q&A category in there [1].
[1] https://github.com/searxng/searxng/discussions/categories/q-a
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>