Remove RouteInfo hidden depdendency in NMS

Update legecy route is replaced by calling INetd directly.
addLegacyRouteForNetId() is no longer needed. This method also
have dependency with the hidden method in RouteInfo which will
be a part of incoming connectivity module. Thus, remove the
addLegacyRouteForNetId() to resolve the dependency.

Bug: 172183305
Test: m ; atest FrameworksNetTests
Change-Id: Ifc561b6dfb45bc51dee244ae114029ae520d8556