Revert "Decouple workspace from call (#3380)"

This reverts commit 6da57cbc6e, reversing
changes made to 62b1843704.

Also, adjust new code that was written using the "call handler".

crates/collab2/src/tests/test_server.rs

@@ -221,7 +221,6 @@ impl TestServer {
             fs: fs.clone(),
             build_window_options: |_, _, _| Default::default(),
             node_runtime: FakeNodeRuntime::new(),
-            call_factory: |_| Box::new(workspace::TestCallHandler),
         });
 
         cx.update(|cx| {