The Send CTRL-ALT-DEL signal, is only available when the SA client is preinstalled in the machines and it is not downloaded.
There is a installer of this tool in the SDM media files in the following path:
Once is installed, it is necessary to change the End-User Client Launch Mode which by default is set to download the launcher.
Go to the End User SA Access list under Administration tab->Security and Role Management->Support Automation Access List->end user, instead off download the launcher, use the pre-installed client.
After this log in with an end user launch live assistance, this time you should not be asked to download the component instead you will be asked to use the client and then it will launch the application.
Then proceed with the analyst console to create a web session and this time after selecting remote control the option to send the CTRL-ALT_DEL should be enabled.