Revert "Resolve MPEGStreamData::Reset() ambiguities."

This reverts commit [e75fb21c45942ee8a17a8d5c64901f2868658440].

This is causing tuning to fail some of the time.

What appears to happen is that MPEGStreamData::SetDesiredProgram()
calls ResetMPEG() when a program number is desired which has not
been seen yet. This cause the ATSC tuning data to also be reset,
which wasn't the case before [e75fb21c45] because of a bug in the
implementation, and this causes tuning to fail.

Refs #11334.