Remove refs to pandoc-discuss from issue templates.

See #10247.

.github/ISSUE_TEMPLATE/config.yml

@@ -2,7 +2,6 @@ blank_issues_enabled: false
 contact_links:
   - name: Ask a question
     url: https://github.com/jgm/pandoc/discussions
-    # https://groups.google.com/forum/#!forum/pandoc-discuss
     about: "Discussion forum for pandoc"
   - name: Contributing Guidelines
     url: https://pandoc.org/CONTRIBUTING.html

.github/ISSUE_TEMPLATE/feature_request.md

@@ -12,7 +12,7 @@ Thank you for suggesting a feature! Before you continue, please make sure that y
 
 - read the contributing guidelines: https://pandoc.org/CONTRIBUTING.html
 - searched the issue tracker for similar issues (including closed issues): https://github.com/jgm/pandoc/issues
-- searched the pandoc-discuss mailing list for relevant discussions: https://groups.google.com/forum/#!forum/pandoc-discuss
+- searched the discussion list for relevant discussions: https://github.com/jgm/pandoc/discussions
 -->
 
 **Describe your proposed improvement and the problem it solves.**