Remove copy-pasted module documentation

It doesn't seem right that both room and room_member have  the same
description. Also room_member is private and doesn't usually show up in
docs.

Author: jplatte

crates/matrix-sdk/src/lib.rs

@@ -53,7 +53,6 @@ pub mod event_handler;
 mod http_client;
 /// High-level room API
 pub mod room;
-/// High-level room API
 mod room_member;
 mod sync;