windows: fix window activate action (#9664)

Now, the window activation event can be triggered correctly. As shown in
the video, when the window is activated, the caret blinks; when the
window loses activation due to me clicking on the PowerShell window, the
caret stops blinking.



https://github.com/zed-industries/zed/assets/14981363/4c1b2bec-319d-4f21-879e-5a0af0a00d8e



Release Notes:

- N/A

crates/gpui/src/platform/windows/platform.rs

@@ -10,7 +10,6 @@ use std::{
     path::{Path, PathBuf},
     rc::Rc,
     sync::{Arc, OnceLock},
-    time::Duration,
 };
 
 use ::util::{ResultExt, SemanticVersion};