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/dap/src/client.rs

@@ -71,7 +71,6 @@ impl DebugAdapterClient {
         let client_id = this.id;
 
         // start handling events/reverse requests
-
         cx.background_spawn(Self::handle_receive_messages(
             client_id,
             server_rx,
@@ -119,7 +118,6 @@ impl DebugAdapterClient {
                 Ok(message) => message,
                 Err(e) => break Err(e.into()),
             };
-
             match message {
                 Message::Event(ev) => {
                     log::debug!("Client {} received event `{}`", client_id.0, &ev);
@@ -164,7 +162,6 @@ impl DebugAdapterClient {
             command: R::COMMAND.to_string(),
             arguments: Some(serialized_arguments),
         };
-
         self.transport_delegate
             .add_pending_request(sequence_id, callback_tx)
             .await;
@@ -434,7 +431,7 @@ mod tests {
 
         let client = DebugAdapterClient::start(
             crate::client::SessionId(1),
-            DebugAdapterName(Arc::from("test-adapter")),
+            DebugAdapterName("test-adapter".into()),
             DebugAdapterBinary {
                 command: "command".into(),
                 arguments: Default::default(),