Revise sound packet time sequencing for a more recent Firefox.

Around version 45, Firefox started being very particular about the
time stamps put into the Opus stream.  The time stamps from the Spice server are
somewhat irregular.  They mostly arrive every 10 ms, but sometimes it is 11, or sometimes
with two time stamps the same in a row.  The previous logic resulted in fuzzy and/or
distorted audio streams in Firefox in a row.

Thus, we end up with an inelegant hack.  Essentially, we force every packet to have
a 10ms time delta, unless there is an obvious gap in time stream, in which case we
will resync.

This replaces logic that mitigated only the duplicated time packets.

The long term solution would appear to be 'sequence' mode, but I cannot get
Firefox to use that mode (and MDN suggests that for codecs such as VP8 with time
stamps in line, that Firefox will not accept it).