Fix unused import in windows code

Author: luna-duclos

browser_windows.go

@@ -2,8 +2,6 @@
 //sys shellExecute(hwnd int, verb string, file string, args string, cwd string, showCmd int) (err error) = shell32.ShellExecuteW
 package browser
 
-import "os/exec"
-
 const sW_SHOWNORMAL = 1
 
 func openBrowser(url string) error {