[10739] Cleanup pet remove code and some fixes.

* Merge Player::RemovePet and Pet::Remove function code to Pet::Unsummon
  This let be sure that in all cases all required steps doen. For example this fix
  creature's guardians propertly remove from guardians list.
* Add new pet save mode PET_SAVE_REAGENTS as replacement PET_SAVE_NOT_IN_SLOT+true-arg stable pair in old function args
  This will avoid use reagent save arg with wrong different save modes.
* Fixed recently added code with absent check for re-summon protector pet call.

src/game/MiscHandler.cpp

@@ -62,7 +62,7 @@ void WorldSession::HandleRepopRequestOpcode( WorldPacket & recv_data )
     }
 
     //this is spirit release confirm?
-    GetPlayer()->RemovePet(NULL,PET_SAVE_NOT_IN_SLOT, true);
+    GetPlayer()->RemovePet(PET_SAVE_REAGENTS);
     GetPlayer()->BuildPlayerRepop();
     GetPlayer()->RepopAtGraveyard();
 }