Removed deprecated methods from INetworkPolicyManager.

Removed the following methods:

- addRestrictBackgroundWhitelistedUid(int uid)
- removeRestrictBackgroundWhitelistedUid(int uid);
- getRestrictBackgroundWhitelistedUids();

They've been replaced by getUidsWithPolicy() and setUidPolicy().

Test: m -j32 FrameworksServicesTests && adb install -r -g ${ANDROID_PRODUCT_OUT}/data/app/FrameworksServicesTests/FrameworksServicesTests.apk && adb shell am instrument -e class "com.android.server.NetworkPolicyManagerServiceTest" -w "com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner"

BUG: 28791717

Change-Id: I8f6a569cef84c2be60e3277756283026c0fb5b29