Backend broadcast payloads for internal_chat.message.deleted and
internal_chat.reaction.deleted used channel_id as the key, but the
frontend ActionCable handlers (and all other internal-chat events)
expect internal_chat_channel_id. This caused deleted messages and
removed reactions to stay visible on screen until a manual refresh.
Rename the key on the backend so the payloads match the convention
shared with message.created/updated and reaction.created, and drop the
defensive fallback on the frontend reaction-deleted handler.
bd61458720