This property was already deprecated in libmm-glib and removed from
the daemon in 1.10, so the counterpart property in MMSimpleStatus
should also be deprecated.
It's pointless to have libmm-common around, just merge it into libmm-glib and
make ModemManager depend on libmm-glib directly. At the end, the non-common
stuff in libmm-glib is really minimal.