Remove telegram, discord, and fakechat plugins (#741)

Remove the three chat bridge plugins from external_plugins/ and their
corresponding entries in marketplace.json.

Co-authored-by: Claude <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -264,12 +264,6 @@
       },
       "homepage": "https://github.com/awslabs/agent-plugins"
     },
-    {
-      "name": "discord",
-      "description": "Discord messaging bridge with built-in access control. Manage pairing, allowlists, and policy via /discord:access.",
-      "category": "productivity",
-      "source": "./external_plugins/discord"
-    },
     {
       "name": "explanatory-output-style",
       "description": "Adds educational insights about implementation choices and codebase patterns (mimics the deprecated Explanatory output style)",
@@ -281,12 +275,6 @@
       "category": "learning",
       "homepage": "https://github.com/anthropics/claude-plugins-public/tree/main/plugins/explanatory-output-style"
     },
-    {
-      "name": "fakechat",
-      "description": "Localhost web chat for testing the channel notification flow. No tokens, no access control, no third-party service.",
-      "category": "development",
-      "source": "./external_plugins/fakechat"
-    },
     {
       "name": "feature-dev",
       "description": "Comprehensive feature development workflow with specialized agents for codebase exploration, architecture design, and quality review",
@@ -976,12 +964,6 @@
         }
       }
     },
-    {
-      "name": "telegram",
-      "description": "Telegram messaging bridge with built-in access control. Manage pairing, allowlists, and policy via /telegram:access.",
-      "category": "productivity",
-      "source": "./external_plugins/telegram"
-    },
     {
       "name": "terraform",
       "description": "The Terraform MCP Server provides seamless integration with Terraform ecosystem, enabling advanced automation and interaction capabilities for Infrastructure as Code (IaC) development.",