[MS48.1] Remove INetworkStatsSession from ChartDataLoader

Replace with public APIs. Since NetworkStatsHistory is no longer
accessible, use List<Bucket> as an alternative structure for
furthur manipulating.

Test: atest clockwork-settings-robotests
      make RunSettingsRoboTests -j40
      make RunSettingsLibRoboTests
           ROBOTEST_FILTER=DataUsageControllerTest
      make RunSettingsLibRoboTests
           ROBOTEST_FILTER=NetworkCycleChartDataLoaderTest
      make RunSettingsLibRoboTests
           ROBOTEST_FILTER=NetworkCycleDataForUidLoaderTest
      make RunSettingsLibRoboTests
           ROBOTEST_FILTER=NetworkCycleDataLoaderTest
      make RunSettingsLibRoboTests
           ROBOTEST_FILTER=DataUsageUtilsTest
Bug: 204830222
Ignore-AOSP-First: Related API conflict, need master first.
Change-Id: I5336ceef43193343d707724066e2da40f1ff0633