tmpfiles: remove old ICE and X11 sockets at boot (systemd#6979)

tmpfiles: remove old ICE and X11 sockets at boot

When not using tmpfs based /tmp, leftover sockets
might prevent X startup. Ensure directory is clean at boot time.

(cherry picked from commit 4a1f92c)

tmpfiles.d/x11.conf

@@ -8,11 +8,12 @@
 # See tmpfiles.d(5) for details
 
 # Make sure these are created by default so that nobody else can
-d /tmp/.X11-unix 1777 root root 10d
-d /tmp/.ICE-unix 1777 root root 10d
-d /tmp/.XIM-unix 1777 root root 10d
-d /tmp/.font-unix 1777 root root 10d
-d /tmp/.Test-unix 1777 root root 10d
+# or empty them at startup
+D! /tmp/.X11-unix 1777 root root 10d
+D! /tmp/.ICE-unix 1777 root root 10d
+D! /tmp/.XIM-unix 1777 root root 10d
+D! /tmp/.font-unix 1777 root root 10d
+D! /tmp/.Test-unix 1777 root root 10d
 
 # Unlink the X11 lock files
 r! /tmp/.X[0-9]*-lock