Comment 0 for bug 1773859

$ sudo apt upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be REMOVED:
  systemd-shim
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 71.7 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 632222 files and directories currently installed.)
Removing systemd-shim (9-1bzr4ubuntu1) ...
Removing 'diversion of /usr/share/dbus-1/system-services/org.freedesktop.systemd1.service to /usr/share/dbus-1/system-services/org.freedesktop.systemd1.service.systemd by systemd-shim'
dpkg-divert: error: rename involves overwriting '/usr/share/dbus-1/system-services/org.freedesktop.systemd1.service' with
  different file '/usr/share/dbus-1/system-services/org.freedesktop.systemd1.service.systemd', not allowed
dpkg: error processing package systemd-shim (--remove):
 subprocess installed post-removal script returned error exit status 2
Errors were encountered while processing:
 systemd-shim
E: Sub-process /usr/bin/dpkg returned an error code (1)

Commenting out the dpkg-divert in systemd-shim's postrm solved this for me and I was about to continue the upgrade.