Revert "UBUNTU: SAUCE: (efi-lockdown) Add a SysRq option to lift kernel lockdown"

Revert "UBUNTU: SAUCE: (efi-lockdown) Add a SysRq option to lift kernel lockdown"

BugLink: https://bugs.launchpad.net/bugs/1861238
This reverts commit 531c25a35b2a93e025e72e04f16b0f3620ace581.

The original intent behind Lockdown's SysRq support was that the SysRq
command to lift Lockdown would only be honored if the command was
physically entered on a keyboard. Attempts to synthetically generate the
SysRq command, by a software program, were to be ignored since software,
even running as root, must not have the authorization to lift Lockdown.

Unfortunately, attempts to detect a synthetic SysRq command can be
thwarted by a privileged process that is able to set up a USB/IP
connection as the USB/IP connection could be used to lift Lockdown.

Remove the ability to lift Lockdown using SysRq.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Sultan Alsawaf <sultan.alsawaf@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>