Remove forcing wallpaper visible for freeform task

Since secondary home and desktop mode (DesktopWallpaperActivity) is
introduced, it no longer needs the special case to make wallpaper
visible for freeform task.
 i.e. Remove I6553c0fcec770e931c08bed8ef5c533b47afe1b8

This reduces looping all tasks when there is no freeform tasks on
a device which supports freeform.

Bug: 433694978
Flag: com.android.window.flags.do_not_force_wallpaper_for_freeform_task
Test: CtsWindowManagerDeviceWindow
Change-Id: Ib10578c1ade6d70117a39722601de5396e4d8bcf