fbsd-from-scratch: remove it

• it references sysinstall, which is gone
• the scripts used to install the system use pkg_add not pkg
• and are rotted in other ways
• the limitations of sysinstall have been somewhat mitigated by

	  bsdinstall (which can install into a new directory)

• it warns of outdated stuff (acroread8 doesn't exist anymore)
• package building takes place on runnning system and not on poudriere
• many of the packages referenced don't exist or are vastly changed
• it incorrectly installs the base system
• and more

Discussed with: jmg, Daniel O'Connor, bjk