[10739] Cleanup pet remove code and some fixes.

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<pre>m src/game/BattleGround.cpp
m src/game/MiscHandler.cpp
m src/game/NPCHandler.cpp
m src/game/Pet.cpp
m src/game/Pet.h
m src/game/PetHandler.cpp
m src/game/Player.cpp
m src/game/Player.h
m src/game/SpellAuras.cpp
m src/game/SpellEffects.cpp
m src/game/Unit.cpp
m src/game/WorldSession.cpp
m src/shared/revision_nr.h
</pre>
<pre style='white-space:pre-wrap;width:81ex'>[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.</pre>




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