Use correct type for showSaveFilePicker

The return type is exposed so we should opt-in to using it directly.
Rather then creating our own wrong override.

Bug: none
Change-Id: Ide86ddfc139394196c740d2f5d0207cb2847805a
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6771902
Reviewed-by: Paul Irish <paulirish@chromium.org>
Commit-Queue: Paul Irish <paulirish@chromium.org>

front_end/global_typings/global_defs.d.ts

diff --git a/front_end/global_typings/global_defs.d.ts b/front_end/global_typings/global_defs.d.ts
index 8e3e8b7..8db1098 100644
--- a/front_end/global_typings/global_defs.d.ts
+++ b/front_end/global_typings/global_defs.d.ts
@@ -57,18 +57,12 @@
 interface Window {
   readonly scheduler: Scheduler;
 
-  showSaveFilePicker(opts: unknown): Promise<FileSystemHandle>;
+  // Chromium only feature so not exposed on TypeScript lib.dom
+  showSaveFilePicker(opts: {
+    suggestedName: string,
+  }): Promise<FileSystemFileHandle>;
 }
 
 interface WorkerGlobalScope {
   readonly scheduler?: Scheduler;
 }
-
-interface FileSystemWritableFileStream extends WritableStream {
-  write(data: unknown): Promise<void>;
-  close(): Promise<void>;
-}
-
-interface FileSystemHandle {
-  createWritable(): Promise<FileSystemWritableFileStream>;
-}