Ticket: #3237

Remove conf/base/etc/rc.conf.local from staging directory for ISO creation.

When we do an upgrade from the CD, the code in build/files/install.sh
calls "/etc/rc.d/dmesg start".  The /etc/rc.d/dmesg script
includes /etc/rc.subr, which in turn sources /etc/rc.conf.local.
When rc.conf.local is sourced, there is code that is unconditionally
run which tries to first query the sqlite database on the NAS box,
and then generate a /var/tmp/rc.conf.freenas config file.
None of this logic should be run from the CD.  So, to fix this remove
rc.conf.local.

The older installer code did this, but we need to remove
conf/base/etc/rc.conf.local as well.  This is necessitated
by some recent changes to the ISO installer, which makes use
of /etc/rc.initdiskless to create memory file systems when booting
from the CD.