Set jni_uses_sdk_apis for NetworkStackTests

NetworkStackTests doesn't set sdk_version but needs portable versions
of its JNI libraries.  Set jni_uses_sdk_apis, and remove the extra
JNI libraries that don't have SDK variants.

(clean cherry-pick from internal branch)
Bug: 154665579
Test: atest NetworkStackCoverageMtsConfigTests on a Q device
Merged-In: Ieff8acec71d206104033a04c049840fd94adfce9
Change-Id: Ieff8acec71d206104033a04c049840fd94adfce9