[Settings] Access ProxySubscriptionManager within DataUsage

Redirect some SubscriptionManager access to ProxySubscriptionManager.
This will reduce some access latency.

Bug: 141833767
Test: manual
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=DataUsageSummaryPreferenceControllerTest
Merged-In: I2cb30dd0570a09543a13ca01cf054ba2d18d70d4
Change-Id: I536b45fd5ddd5d9d9591a133a0f79227a670d7dd