Use std::function

Replace CallableHolder with std::function.  No need to re-invent
the wheel.

Change-Id: I2647a802237dba4a48187718f0d3da59e97575d7
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/manager.cpp b/manager.cpp
index 7d0e7d3..94748ad 100644
--- a/manager.cpp
+++ b/manager.cpp
@@ -165,14 +165,14 @@
 
     for (auto& f : event)
     {
-        if (!(*f)(_bus, msg, *this))
+        if (!f(_bus, msg, *this))
         {
             return;
         }
     }
     for (auto& action : actions)
     {
-        (*action)(_bus, *this);
+        action(_bus, *this);
     }
 }