remove install method fallback from default recipe
remove install method fallback from default recipe

The default install method for any platform not specifically set via
the conditional in the attributes will be `source`, so we don’t need to
have this else branch.

jtimberman/djbdns,jordant/djbdns,jtimberman/djbdns,tas50/djbdns,tas50/djbdns,tas50/djbdns,jordant/djbdns,jordant/djbdns,jtimberman/djbdns