Follow the steps

Setup

Open terminal/putty window
Edit content.ini.append.php

$ vi ezpublish_legacy/settings/override/content.ini.append.php

Add the following

[VersionManagement]
InternalDraftsDuration
InternalDraftsDuration[days]=0
InternalDraftsDuration[seconds]=5

Clear the cache

$ php ezpublish/console cache:clear --env=prod

Test

Access to your site frontpage
Click on "Register" on the top screen
Fill in the fields but DON'T PRESS REGISTER button
Back to the terminal runcronjobs.php

$ php ezpublish/console ezpublish:legacy:script runcronjobs.php

Verify you get something like

Running cronjobs/internal_drafts_cleanup.php at: 13/05/2014 10:49 am
Cleaning up internal drafts...
Cleaned up 1 internal drafts
Completing cronjobs/internal_drafts_cleanup.php at: 13/05/2014 10:49 am
Elapsed time: 00:00:01

Back to your browser press on the "register" button
Verify that you get

Register user
Input did not validate

First name: Input required.
Last name: Input required.
User account: Input required.

Click on /user/register on the top menu
You'll get eZ Demo without the registration form