Remove chroot() from gdnsd

Direct support for chroot() seems outmoded by more modern
and complete container solutions that would be configured
and setup outside of the daemon code itself.  Removing
direct chroot() support kills a fair amount of code/docs
complexity and frees us from having to make any more excuses
about why it doesn't quite work right out of the box under
certain conditions or system configurations.

From the perspective of a user who wasn't using chroot()
anyways, the primary visible change is the replacement
of the "-d rootdir" commandline argument with "-c configfile"