MythMusic: rip out the CDWatcherThread

We will use the media monitor instead now it seems to be more stable.
MythMusic: remove some redundant CD stuff from PlaylistContainer
Coverity warning: if a cast failed, ConnectBackend() will be called with a null.
Likelihood of 0.1%, but there was once a compiler bug that did this for events.
Coverity: m_SendEvent not init'd after 972a8d2d14056689a056d592954fde8838588b28
(which removed it from everywhere except OS X code)
Coverity: "Structurally dead code."
Since about a year ago in the UTC merge(?), checkTimeZone() has done nothing,
which means some helper static functions can also go.
Merge remote-tracking branch 'upstream/master'