Ditch `LLEventTrackable` aka `boost::signals2::trackable`.

Remove documented `LLEventPump` support for `LLEventTrackable`. That claimed
support was always a little bit magical/fragile. IF:

* a class included `LLEventTrackable` as a base class AND
* an instance of that class was managed by `boost::shared_ptr` AND
* you passed one of that class's methods and the `boost::shared_ptr`
  specifically to `boost::bind()` AND
* the resulting `boost::bind()` object was passed into `LLEventPump::listen()`

THEN the promise was that on destruction of that object, that listener would
automatically be disconnected -- instead of leaving a dangling pointer bound
into the `LLEventPump`, causing a crash on the next `LLEventPump::post()` call.

The only existing code in the viewer code base that exercised `LLEventTrackable`
functionality was in test programs. When the viewer calls `LLEventPump::listen()`,
it typically stores the resulting connection object in an `LLTempBoundListener`
variable, which guarantees disconnection on destruction of that variable.

The fact that `LLEventTrackable` support is specific to `boost::bind()`, that it
silently fails to keep its promise with `std::bind()` or a lambda or any other
form of C++ callable, makes it untrustworthy for new code.

Note that the code base still uses `boost::signals2::trackable` for other
`boost::signals2::signal` instances not associated with `LLEventPump`. We are
not changing those at this time.

1 files changed, 1 insertions, 1 deletions

diff --git a/indra/newview/llspeakers.h b/indra/newview/llspeakers.h
index 234de42953..d3304dba59 100644
--- a/indra/newview/llspeakers.h
+++ b/indra/newview/llspeakers.h
@@ -37,7 +37,7 @@ class LLSpeakerMgr;
 class LLAvatarName;
 
 // data for a given participant in a voice channel
-class LLSpeaker : public LLRefCount, public LLOldEvents::LLObservable, public LLHandleProvider<LLSpeaker>, public boost::signals2::trackable
+class LLSpeaker : public LLRefCount, public LLOldEvents::LLObservable, public LLHandleProvider<LLSpeaker>
 {
 public:
     typedef enum e_speaker_type