Remove /docs slash command (#36325)

This PR removes the `/docs` slash command.

We never fully shipped this—with it requiring explicit opt-in via a
setting—and it doesn't seem like the feature is needed in an agentic
world.

Release Notes:

- Removed the `/docs` slash command.

crates/agent_ui/src/agent_ui.rs

@@ -242,7 +242,6 @@ pub fn init(
         client.telemetry().clone(),
         cx,
     );
-    indexed_docs::init(cx);
     cx.observe_new(move |workspace, window, cx| {
         ConfigureContextServerModal::register(workspace, language_registry.clone(), window, cx)
     })
@@ -409,12 +408,6 @@ fn update_slash_commands_from_settings(cx: &mut App) {
     let slash_command_registry = SlashCommandRegistry::global(cx);
     let settings = SlashCommandSettings::get_global(cx);
 
-    if settings.docs.enabled {
-        slash_command_registry.register_command(assistant_slash_commands::DocsSlashCommand, true);
-    } else {
-        slash_command_registry.unregister_command(assistant_slash_commands::DocsSlashCommand);
-    }
-
     if settings.cargo_workspace.enabled {
         slash_command_registry
             .register_command(assistant_slash_commands::CargoWorkspaceSlashCommand, true);