chore(windows): fully disable auto start task

If the registry setting `HKCU\Software\Keyman
Engine\Debug:Flag_UseAutoStartTask[REG_WORD]` is not `0`, then the this
will enable the restart task. Otherwise, all aspects of it are disabled.

For Keyman 14.0 initial release, we will have this flag disabled. If we
can improve stability of it, we'll consider turning it on.