vncserver: extract ForgetSelectedDe()

unix/vncserver

@@ -727,11 +727,14 @@ sub AskUserToChooseDeOrManualXstartup {
     return;
   }
 
-  unlink $de_was_selected_file;
-
+  &ForgetSelectedDe();
   system($selectDeCmd) == 0 || die("Failed to execute $selectDeCmd\n");
 }
 
+sub ForgetSelectedDe {
+  unlink $de_was_selected_file;
+}
+
 sub DetectDisplayNumberFromCliArgs {
   if (@ARGV == 0) {
     return;