Clean up shouldHideSubscription API

Combine shouldHideSubscription and isInvisibleSubscription
for better readability.

Bug: 126637721
Test: manual - use test app to call SubscriptionManager APIs to make
sure they return correct values.

Change-Id: I0deb463430a6825db40ec00abac49cb662e79437
Merged-In: I0deb463430a6825db40ec00abac49cb662e79437