Stop copying directly-connected routes to the main table, #2.

For a long time we have thought that copying directly-connected
routes to the main table was necessary to add gatewayed routes
to other routing tables. However, this is not necessary when the
directly-connected routes are properly created with "scope link"
as we do in http://ag/513100 .

Delete the copying code, but don't delete the rule that looks up
the main table or the code that dumps it. The main table is used
for things like cell networking, because the RIL emulates cell
networks, which are actually point-to-point, as directly
connected broadcast subnets (e.g., a /30 or a /27) with a fake
default gateway.  The directly-connected route that covers the
fake default gateway is implicitly created by adding the IP
address, but it's in the main table, so we can't add the default
route without looking up the main table.

Change-Id: I93bd4764ac75fdcc98fa4206c601524100d53fc3