MT#59962 Coverity Scan: Uninitialized pointer field (reg_agent)

Remove `uac_auth_f` from `RegistrationAgentFactory`,
not used.

Fixes:

    Uninitialized pointer field (UNINIT_CTOR).
    uninit_member: Non-static class member uac_auth_f
    is not initialized in this constructor nor in any functions that it calls.

Change-Id: I3e8d0703d8bd7226369248bd87c1449f97e7ac6a

apps/reg_agent/RegistrationAgent.h

@@ -64,7 +64,6 @@ class RegThread : public AmThread {
 class RegistrationAgentFactory: public AmSessionFactory
 {
   RegThread dialer;    
-  AmSessionEventHandlerFactory* uac_auth_f;
 
  public:
   RegistrationAgentFactory(const string& _app_name);