Core/Instances: Fix exploit too much players in instances/raids
Merge pull request #11377 from Yelvann/master

Core/Instances: Fix exploit too much players in instances/raids
Core/Player: Fix compile error introduced in ##11377 merge
Core/Entities: Fix combat state setting when FFA PvP flag is set

Description:
Currently there is an issue, when you are in FFA areas, but you dont have PvP flag activated.

You should get the PvP-In-Combat delay timer, but instead you just get the usual timer as if you would not fight in PvP.

Reproduction:
1) Get two players in FFA area Gurubashi arena down in the battle area (.tele Gurubashi)

2) Fight each other

3) When stopping combat, the combat state will switch off immediately. But it is supposed to switch off after some delay, because it was a PvP fight.

Closes #11103

Signed-off-by: Duarte Duarte <dnpd.dd@gmail.com>
Core/Instances: Fix memory leak in InstanceSaveMgr

Fix memory leak in InstanceSaveMgr added in 1f170c99efec6c89b9a454a3aa17511341f61659 .
Make InstanceSave::SetToDelete() private since it's not supposed to be used by anything other than InstanceSave or its friend class InstanceSaveMgr .