Scripts/SmartAI: Some clean-up work:

- NULL -> nullptr
- Rename "AssistPlayerInCombat(who)" to "AssistPlayerInCombatAgainst(who)" to reflect what the method actually does
- Code style

No functionality was changed.

src/server/game/AI/SmartScripts/SmartScript.cpp

@@ -3613,36 +3613,6 @@ void SmartScript::OnMoveInLineOfSight(Unit* who)
 
     ProcessEventsFor(me->IsInCombat() ? SMART_EVENT_IC_LOS : SMART_EVENT_OOC_LOS, who);
 }
-
-/*
-void SmartScript::UpdateAIWhileCharmed(const uint32 diff) { }
-
-void SmartScript::DoAction(const int32 param) { }
-
-uint32 SmartScript::GetData(uint32 id)
-{
-    return 0;
-}
-
-void SmartScript::SetData(uint32 id, uint32 value) { }
-
-void SmartScript::SetGUID(uint64 guid, int32 id) { }
-
-uint64 SmartScript::GetGUID(int32 id)
-{
-    return 0;
-}
-
-void SmartScript::MovepointStart(uint32 id) { }
-
-void SmartScript::SetRun(bool run) { }
-
-void SmartScript::SetMovePathEndAction(SMART_ACTION action) { }
-
-uint32 SmartScript::DoChat(int8 id, uint64 whisperGuid)
-{
-    return 0;
-}*/
 // SmartScript end
 
 Unit* SmartScript::DoSelectLowestHpFriendly(float range, uint32 MinHPDiff)