doc: remove .github/ISSUE_TEMPLATE.md in favor of the template folder

This removes the obsolete issue template file since we already
have the issue template folder which is the one currently in effect.

PR-URL: https://github.com/nodejs/node/pull/31656
Refs: https://github.com/nodejs/node/pull/31611


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>