Move service name duplication lookup to EndSection

This is paving the way to allow an "override" tag
in init services. This also means that errors for
part of a service definition in its section will
be shown in addition to the fact that the service
is duplicated.

Bug: 69050941
Test: boot, init_tests
Change-Id: Ic1ea8597789f45ead1083451b3e933db1524bdc9