AnotherPacketSource: make getBufferedDurationUs more discontinuity-aware

The new getBufferedDurationUs implementation obsoletes the purpose of
getEstimatedDurationUs; remove getEstimatedDurationUs and its
associated member variables. Finally replace calls to
getEstimatedDurationUs with getBufferedDurationUs.

Change-Id: I38f20df8e177ffbfe299b203d99076fc98dcd274
3 files changed