Scripts/CoS: removed SetDespawnAtFar, fixed situation when Artas attacked some NPC and disappeared because he was out of range of players

With these lines it's almost impossible to finish properly this dungeon. For example when Arthas moves ahead to attack NPC and then returns back, when this happens, Arthas is despawned.
DB/SAI: Clear param2 for Remove Aura

Clear exististing data in param2 for sai entries using smart_action 28 as these param was previously unused but some lines of sai still had this param > 0
Core/SAI: Allow dropping a specific amount of aura charges using SMART_ACTION_REMOVEAURASFROMSPELL (action_param2).

(cherry picked from commit ed4feec276bd395715c23c58b74a6dae4198039b)
Merge pull request #13432 from bloerwald/fix_compiler_detection_on_unix

cmake: platform: also detect clang by C_COMPILER_ID: C_COMPILER may vary
(cherry picked from commit 774e22ec4a8859664ace0a532c2ab4ae220e5cc9)