debugger: Remove fake adapter and un-gate GDB (#27557)

This is a clean-up PR in anticipation of introduction of Debugger
Registry. I wanna get rid of DebugAdapterKind (or rather, it being an
enum).
Release Notes:

- N/A

---------

Co-authored-by: Anthony Eid <hello@anthonyeid.me>
Co-authored-by: Anthony <anthony@zed.dev>

crates/recent_projects/src/ssh_connections.rs

@@ -557,6 +557,7 @@ pub async fn open_ssh_project(
                 app_state.node_runtime.clone(),
                 app_state.user_store.clone(),
                 app_state.languages.clone(),
+                app_state.debug_adapters.clone(),
                 app_state.fs.clone(),
                 None,
                 cx,