[8793] Don't do operations through singleton if already in singleton context.

* Also, some minor things:
   - Remove duplicate sWorldLog define.
   - Add sRealmList macro for RealmList::Instance().
   - Use sLog macro in scripting log functions.

src/realmd/RealmList.cpp

@@ -33,7 +33,7 @@ RealmList::RealmList( ) : m_UpdateInterval(0), m_NextUpdateTime(time(NULL))
 {
 }
 
-RealmList& RealmList::Instance()
+RealmList& sRealmList
 {
     static RealmList realmlist;
     return realmlist;