DO NOT MERGE Disable the NetworkStackNext and NetworkStackNextTests

Disable the NetworkStackNext and NetworkStackNextTests targets in
mainline-prod. They're technically not needed in mainline-prod since
we don't ship them, and the new API is only used in these.

Bug: 175609674
Test: Compiles
Ignore-AOSP-First: Isolated change to mainline-prod
Change-Id: Id0ed6e5b2eda50fcf7be2b1209f7a3d1a5a25c9f