Stop setting the legacy net.dnsX system properties

These have been locked down via SELinux for a while and thus
they should be safe to delete at this point.

Test: atest FrameworksNetTest
Bug: 33308258
Bug: 148724751
Change-Id: I3a1e9c6ad92c8d2367e0048e5d6cd7d06bbc6e80
3 files changed