Playground: remove unnecessary check

Because we want to pre load everything, we should allow the system to make channel objects even if we don’t have local data for them yet. We do the same thing with members.

packages/sdk/src/sync-agent/spaces/models/space.ts

@@ -111,9 +111,6 @@ export class Space extends PersistedObservable<SpaceModel> {
     }
 
     getChannel(channelId: string): Channel {
-        if (!this.data.channelIds.includes(channelId)) {
-            throw new Error(`channel ${channelId} not found in space ${this.data.id}`)
-        }
         if (!this.channels[channelId]) {
             this.channels[channelId] = new Channel(
                 channelId,