(maint) Remove unneeded options for 'apt-get update'

Previously apt-get update was invoked with the -y -f -m
options. None of these options actually make sense for *update*
(though -y makes total sense for *install*). Starting with
trusty's apt-get, apt-get actually rejects (at least) -f for
apt-get install.

So this patch simply removes those unneeded options.