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/remote_server/src/remote_editing_tests.rs

@@ -4,6 +4,7 @@
 use crate::headless_project::HeadlessProject;
 use client::{Client, UserStore};
 use clock::FakeSystemClock;
+use dap::DapRegistry;
 use extension::ExtensionHostProxy;
 use fs::{FakeFs, Fs};
 use gpui::{AppContext as _, Entity, SemanticVersion, TestAppContext};
@@ -1445,6 +1446,7 @@ pub async fn init_test(
     let http_client = Arc::new(BlockedHttpClient);
     let node_runtime = NodeRuntime::unavailable();
     let languages = Arc::new(LanguageRegistry::new(cx.executor()));
+    let debug_adapters = DapRegistry::default().into();
     let proxy = Arc::new(ExtensionHostProxy::new());
     server_cx.update(HeadlessProject::init);
     let headless = server_cx.new(|cx| {
@@ -1457,6 +1459,7 @@ pub async fn init_test(
                 http_client,
                 node_runtime,
                 languages,
+                debug_adapters,
                 extension_host_proxy: proxy,
             },
             cx,