Make FlaggedAPI available to CtsThreadNetworkTestCases

FlaggedAPI will be ignored in udc-mainline-prod.
This makes CtsThreadNetworkTestCases build fail.
This CL updates CtsThreadNetworkTestCases to build against FlaggedAPI
and also updates framework-connectivity-jarjar-rules not to jarjar
FlaggedAPI.

Test: TH
Test: m CtsThreadNetworkTestCases
Change-Id: Ida8872b3bf61b7a59733f5fcec9e7d250efd3e58