* Use kdesu instead of pkexec. (pkexec may work too in Tumbleweed.)

Because if we use pkexec, we get error in openSUSE Leap 15:
QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
No protocol specified
No protocol specified
qt.qpa.screen: QXcbConnection: Could not connect to display :0
Could not connect to any X display.

If we use pkexec, sometimes (in Tumbleweed) Calamares may have theme issues.

diff --git a/calamares.desktop b/calamares.desktop
--- a/calamares.desktop
+++ b/calamares.desktop
@@ -5,7 +5,7 @@
 GenericName=System Installer
 Keywords=calamares;system;installer;
 TryExec=calamares
-Exec=sh -c "pkexec calamares"
+Exec=kdesu -c /usr/bin/calamares
 Comment=Calamares — System Installer
 Icon=calamares
 Terminal=false