chore: Remove slack channel (#1097)

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +0,0 @@
-blank_issues_enabled: false
-contact_links:
-  - name: Support & usage queries
-    url:  https://vscode-dev-community.slack.com/archives/C011NUFTHLM
-    about: For general support queries please use this slack channel