github: Remove references to matrix chats

Forgotten in 2ed8dd12

.github/ISSUE_TEMPLATE/config.yml

@@ -1,8 +1,5 @@
 blank_issues_enabled: false
 contact_links:
-  - name: Matrix
-    url: https://matrix.to/#/#ckb-next:matrix.org
-    about: "Ask for support in the #ckb-next room."
   - name: IRC
     url: https://web.libera.chat/?channels=#ckb-next
     about: "Ask for support in #ckb-next at web.libera.chat."

.github/ISSUE_TEMPLATE/help-request.yml

@@ -7,7 +7,6 @@ body:
       value: |
         ## Please try these Resources first!
         * IRC chat: #ckb-next channel at [irc.libera.chat](https://web.libera.chat/?channels=#ckb-next)
-        * [Matrix](https://matrix.to/#/#ckb-next:matrix.org): #ckb-next:matrix.org
   - type: textarea
     id: question-body
     attributes: