Revert "app: [Windows] suppress double-click behaviour for custom decorations"

This reverts commit 82cbb7b8da.

As Egon Elbre points out in

https://todo.sr.ht/~eliasnaur/gio/600#event-377179

this is not the right fix.

app/internal/windows/windows.go

@@ -266,7 +266,6 @@ const (
 	WM_MOUSEWHEEL           = 0x020A
 	WM_MOUSEHWHEEL          = 0x020E
 	WM_NCACTIVATE           = 0x0086
-	WM_NCLBUTTONDBLCLK      = 0x00A3
 	WM_NCHITTEST            = 0x0084
 	WM_NCCALCSIZE           = 0x0083
 	WM_PAINT                = 0x000F

app/os_windows.go

@@ -326,12 +326,6 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 		mi := windows.GetMonitorInfo(w.hwnd)
 		szp.Rgrc[0] = mi.WorkArea
 		return 0
-	case windows.WM_NCLBUTTONDBLCLK:
-		if !w.config.Decorated {
-			// Override Windows behaviour when we
-			// draw decorations.
-			return 0
-		}
 	case windows.WM_PAINT:
 		w.draw(true)
 	case windows.WM_SIZE: