Delete the last remaining user of TestNetworkStackLib.

FrameworksNetIntegrationTests is the last user of this target.
It is not really necessary since it can trivially be replaced by
NetworkStackApiStableLib.

Bug: 167645754
Test: atest FrameworksNetIntegrationTests
Change-Id: Id5e8eb3f58590f4b3cfbcbef66b00acbba77a7a7