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>

external_plugins/fakechat/README.md

@@ -1,47 +0,0 @@
-# fakechat
-
-Simple UI for testing the channel contract without an
-external service. Open a browser, type, messages go to your Claude Code
-session, replies come back.
-
-
-## Setup
-
-These are Claude Code commands — run `claude` to start a session first.
-
-Install the plugin:
-```
-/plugin install fakechat@claude-plugins-official
-```
-
-**Relaunch with the channel flag** — the server won't connect without this. Exit your session and start a new one:
-
-```sh
-claude --channels plugin:fakechat@claude-plugins-official
-```
-
-The server prints the URL to stderr on startup:
-
-```
-fakechat: http://localhost:8787
-```
-
-Open it. Type. The assistant replies in-thread.
-
-Set `FAKECHAT_PORT` to change the port.
-
-## Tools
-
-| Tool | Purpose |
-| --- | --- |
-| `reply` | Send to the UI. Takes `text`, optionally `reply_to` (message ID) and `files` (absolute path, 50MB). Attachment shows as `[filename]` under the text. |
-| `edit_message` | Edit a previously-sent message in place. |
-
-Inbound images/files save to `~/.claude/channels/fakechat/inbox/` and the path
-is included in the notification. Outbound files are copied to `outbox/` and
-served over HTTP.
-
-## Not a real channel
-
-There's no history, no search, no access.json, no skill. Single browser tab,
-fresh on every reload. This is a dev tool, not a messaging bridge.