[WIFI] Remove System APIs overlays added as part of Wi-Fi mainline

The removed 4 overlays are unnecessarily shared between connectivity
and Wi-Fi: there's no reason or requirement to assume they are
identical.

Having them as System API would necessitate a formal API - getters.

Therefore, remove them as System API. Duplicate them within the Wi-Fi
mainline module.

Bug: 144764992
Test: atest android.net.wifi
Test: atest ConnectivityServiceTest
Test: atest com.android.server.wifi
Change-Id: Ic5d1076cab5210eef17c2672d06e2566449939c2