MT#62508 services: Remove any systemd broken service symlinks

Before running «systemctl preset-all» we remove all .wants dependency
directories, because otherwise the preset-all command leaves obsolete
files behind. But «systemctl preset-all» fails if there's any broken
service symlink around, which means we end up with no dependency
information whatsoever implying a severely broken system, that in
addition is then unbootable.

Remove any such broken symlinks before calling «systemctl preset-all».

Change-Id: I58fe650cb04ddb140922563169a7fedb09a8ceac
(cherry picked from commit a09d8f42e2)
(cherry picked from commit b2b4ffb402)

scripts/services

@@ -145,6 +145,10 @@ systemd_daemon_reload_preset() {
     log_debug "Running: systemctl daemon-reload 2>&1 || true"
     systemctl daemon-reload 2>&1 || true
 
+    log_debug "Removing any broken systemd service symlink"
+    find -L /etc/systemd/system -type l \
+      | xargs -r rm
+
     log_debug "systemd needs preset-all to enable/disable services (to start them on boot)"
     log_debug "Running: rm -rf /etc/systemd/system/*.wants/ || true"
     rm -rf /etc/systemd/system/*.wants/ || true