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, 2 insertions, 2 deletions

diff --git a/indra/viewer_components/login/tests/lllogin_test.cpp b/indra/viewer_components/login/tests/lllogin_test.cpp
index 8aea3b37aa..f051f8c67f 100644
--- a/indra/viewer_components/login/tests/lllogin_test.cpp
+++ b/indra/viewer_components/login/tests/lllogin_test.cpp
@@ -66,7 +66,7 @@
 *   Helper classes
 *****************************************************************************/
 // This is a listener to receive results from lllogin.
-class LoginListener: public LLEventTrackable
+class LoginListener
 {
     std::string mName;
     LLSD mLastEvent;
@@ -137,7 +137,7 @@ public:
     }
 };
 
-class LLXMLRPCListener: public LLEventTrackable
+class LLXMLRPCListener
 {
     std::string mName;
     LLSD mEvent;