shared: Drop 'name=' prefix from SYSTEMD_CGROUP_CONTROLLER define.

In cgtop,mount-setup,nspawn the name= prefix is hard-coded in the
mount options, and the define is not used.

Everywhere else, we explicitly white-list allow 'name=' prefix to be
used with all controllers, and strip it out to 'normalise' the
controller name. That work is mostly inflicted on us due to 'name='
prefix in the define. Dropping this prefix makes everything more sane
overall.