Fix incomplete type aegis::channel caused by this include (#72)

Fix for get_channel() getting incomplete type aegis::channel on message.cpp (by removing unnecessary include on channel.hpp)

Author: Lohkdesgds

include/aegis/channel.hpp

@@ -15,7 +15,6 @@
 #include "aegis/ratelimit/ratelimit.hpp"
 #include "aegis/permission.hpp"
 #include "aegis/snowflake.hpp"
-#include "aegis/gateway/objects/messages.hpp"
 #include "aegis/gateway/objects/permission_overwrite.hpp"
 #include "aegis/gateway/objects/channel.hpp"
 #include <shared_mutex>