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

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

BugLink: https://bugs.launchpad.net/bugs/1861238
This reverts commit de4a78d3b642e5504b28e901b07eb4da6784dd3d.

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>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>