remove redundant fields from slack alert destination (#5514)

redash/destinations/slack.py

@@ -12,12 +12,8 @@ def configuration_schema(cls):
             "type": "object",
             "properties": {
                 "url": {"type": "string", "title": "Slack Webhook URL"},
-                "username": {"type": "string", "title": "Username"},
-                "icon_emoji": {"type": "string", "title": "Icon (Emoji)"},
-                "icon_url": {"type": "string", "title": "Icon (URL)"},
-                "channel": {"type": "string", "title": "Channel"},
             },
-            "secret": ["url"]
+            "secret": ["url"],
         }
 
     @classmethod
@@ -56,15 +52,6 @@ def notify(self, alert, query, user, new_state, app, host, options):
 
         payload = {"attachments": [{"text": text, "color": color, "fields": fields}]}
 
-        if options.get("username"):
-            payload["username"] = options.get("username")
-        if options.get("icon_emoji"):
-            payload["icon_emoji"] = options.get("icon_emoji")
-        if options.get("icon_url"):
-            payload["icon_url"] = options.get("icon_url")
-        if options.get("channel"):
-            payload["channel"] = options.get("channel")
-
         try:
             resp = requests.post(
                 options.get("url"), data=json_dumps(payload), timeout=5.0