Change 'idx' to 'index' for SubscriptionManager api.

Bug: 35767068
Test: No build failure on update.
Change-Id: I56977b047512100d5fbe7eb8eb2df8aa1f773b8b
Merged-in: I56977b047512100d5fbe7eb8eb2df8aa1f773b8b
9 files changed