Remove stale references to Rocket Chat. (#3142)

Also, check in a cleaner version of the logo.

content/_index.md

@@ -9,7 +9,7 @@ title: Istio
         "logo": "https://istio.io/img/logo.png",
         "sameAs": [
             "https://twitter.com/IstioMesh",
-            "https://istio.rocket.chat/"
+            "https://discuss.istio.io/"
         ]
     }
 </script>

content/blog/2018/announcing-1.0/index.md

@@ -43,8 +43,8 @@ While this is a significant milestone for the project there’s lots more to do.
 
 ## Getting Started
 
-If you’re new to Istio and looking to use it for your deployment we’d love to hear from you. Take a look at [our docs](/docs/), stop by our
-[chat forum](https://istio.rocket.chat) or reach out on the [mailing list](https://groups.google.com/forum/#!forum/istio-dev). If you’d like
+If you’re new to Istio and looking to use it for your deployment we’d love to hear from you. Take a look at [our docs](/docs/) or stop by our
+[chat forum](https://discuss.istio.io). If you’d like
 to go deeper and [contribute to the project](/about/community) come to one of our community meetings and say hello.
 
 ## Finally

content/help/faq/general/how-to-join-slack.md

@@ -6,5 +6,3 @@ weight: 180
 Istio Slack is restricted to Istio Developers. See the [Community Roles](https://github.com/istio/community/blob/master/ROLES.md#member)
 guide, specifically the **Member** role. In this page you can find instructions on how to apply for Istio membership.
 If your membership request has been approved, you will be invited to join the Istio Slack workspace.
-
-All users can interact in a real time chat using [Rocket Chat](https://istio.rocket.chat) though.

content_zh/_index.md

@@ -9,7 +9,7 @@ title: Istio
         "logo": "https://istio.io/img/logo.png",
         "sameAs": [
             "https://twitter.com/IstioMesh",
-            "https://istio.rocket.chat/"
+            "https://discuss.istio.io/"
         ]
     }
 </script>

content_zh/help/faq/general/how-to-join-slack.md

@@ -6,5 +6,3 @@ weight: 180
 Istio Slack 仅限于 Istio 开发人员。
 参见[社区角色](https://github.com/istio/community/blob/master/ROLES.md#member)指南，特别是 **Member** 角色部分。
 在本页您可以找到如何申请 Istio 会员资格的说明。如果您的会员申请被批准，您将会被邀请加入 Istio Slack 工作空间。
-
-所有用户都可以使用 [Rocket Chat](https://istio.rocket.chat) 进行实时聊天。