[screenlocker] Get rid of libkworkspace dependency from the ksld

From the KDisplayManager code :

// This only tells KDM to not auto-re-login upon session crash
void
KDisplayManager::setLock(bool on)
{
    if (DMType == NewKDM || DMType == OldKDM)
        exec(on ? "lock\n" : "unlock\n");
}

Given we no longer have kdm in Plasma 5. This hardly makes sense.

REVIEW: 125837

ksmserver/screenlocker/CMakeLists.txt

@@ -39,7 +39,6 @@ ecm_add_wayland_server_protocol(ksld_SRCS
 add_library(screenlocker_static STATIC ${ksld_SRCS})
 
 target_link_libraries(screenlocker_static
-   PW::KWorkspace
    Qt5::X11Extras
    KF5::I18n
    KF5::IconThemes

ksmserver/screenlocker/ksldapp.cpp

@@ -30,8 +30,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <config-ksmserver.h>
 #include <config-X11.h>
 #include "waylandserver.h"
-// workspace
-#include <kdisplaymanager.h>
 // KDE
 #include <KActionCollection>
 #include <KAuthorized>
@@ -366,7 +364,6 @@ void KSldApp::lock(EstablishLock establishLock)
         return;
     }
 
-    KDisplayManager().setLock(true);
     KNotification::event(QStringLiteral("locked"),
                          i18n("Screen locked"),
                          QPixmap(),
@@ -526,7 +523,6 @@ void KSldApp::doUnlock()
     m_lockedTimer.invalidate();
     m_greeterCrashedCounter = 0;
     endGraceTime();
-    KDisplayManager().setLock(false);
     m_waylandServer->stop();
     KNotification::event(QStringLiteral("unlocked"),
                          i18n("Screen unlocked"),