Fix client-feature, no-model compiles
Fix client-feature, no-model compiles

Some of the methods used in the client dispatch, namely `Channel::id`
and `Message::transform_content`, are not _required_ for functionality
by the dispatcher. Since these methods are `model` features, they can be
gated behind a `model` feature cfg.

Lakelezz/serenity,Roughsketch/serenity,Flat/serenity,acdenisSK/serenity,zeyla/serenity,zeyla/serenity.rs