Now that 5c47e5f6 "fdo#51252 Disable copying
share/prereg/bundled to avoid startup crashes" removed the use of share/prereg,
there is no longer need to generate it in the first place (by calling "unopkg
sync" at build or installation time), and so no need for the "unopkg sync" sub-
command, either.  This also allows to simplify some of the jvmfwk code that was
only there so that "unopkg sync" (which can require a JVM) can work in "hostile"
environments (during build and installation).

Change-Id: I52657384f4561bf27948ba4f0f88f4498e90987f