[Testing] Use AndroidJUnit4 instead in CellDataPreferenceTest

1. Use AndroidJunit4 instead of RobolectricTestRunner
2. Use ApplicationProvider instead of RuntimeEnvironment to get context
3. Change Copy Right
4. Remove the PreferenceViewHolder that not used in test
5. Remove the ProxySubscriptionManager that can get the real object by
context

Bug: 168767478
Test: atest -c CellDataPreferenceTest
Change-Id: I1fa5747c8c6d224d6b13f1a693ff88e57fd150d3