Remove docs for CIDER feature

See https://github.com/matrix-org/matrix-react-sdk/pull/3519

docs/labs.md

@@ -46,11 +46,6 @@ Once enabled, send a custom state event to a room to set values:
 
 That's it. Now should see your new counter under the header.
 
-## New simple composer (`feature_cider_composer`)
-
-An experimental, faster, message composer which should be more reliable and less prone to problems when 
-using your chosen input method.
-
 ## Multiple integration managers (`feature_many_integration_managers`)
 
 Exposes a way to access all the integration managers known to Riot. This is an implementation of [MSC1957](https://github.com/matrix-org/matrix-doc/pull/1957).

riot.im/develop/config.json

@@ -28,7 +28,6 @@
         "feature_sas": "labs",
         "feature_room_breadcrumbs": "labs",
         "feature_state_counters": "labs",
-        "feature_cider_composer": "labs",
         "feature_many_integration_managers": "labs"
     },
     "welcomeUserId": "@riot-bot:matrix.org",