Release mDrmManagerClient in PduPersister release

In Mms test log we found StrictMode printed out DrmManagerClient was
not released, it was created in PduPersister constructor.

To fix this problem, call mDrmManagerClient.release in PduPersister.
release.

Bug: 143230740
Test: Edit and send MMS, not print this log again.
Change-Id: If3318c8e77d6272b9d83af57d910951055356d99