<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def del_windows_env_var(key):
 """Delete an env var. Raises: WindowsError """


    if not isinstance(key, text_type):
        raise TypeError("%r not of type %r" % (key, text_type))

    status = winapi.SetEnvironmentVariableW(key, None)
    if status == 0:
        raise ctypes.WinError()