[Cleanup] Remove Unused Mod Hooks (#2856)

- Removes old `mod_` hooks that have gone unused for years in favor of Lua mods.

zone/spells.cpp

@@ -478,8 +478,6 @@ bool Mob::DoCastSpell(uint16 spell_id, uint16 target_id, CastingSlot slot,
 		return(true);
 	}
 
-	cast_time = mod_cast_time(cast_time);
-
 	// ok we know it has a cast time so we can start the timer now
 	spellend_timer.Start(cast_time);
 
@@ -2819,9 +2817,6 @@ int Mob::CalcBuffDuration(Mob *caster, Mob *target, uint16 spell_id, int32 caste
 		res = 10000; // ~16h override
 	}
 
-
-	res = mod_buff_duration(res, caster, target, spell_id);
-
 	LogSpells("Spell [{}]: Casting level [{}], formula [{}], base_duration [{}]: result [{}]",
 		spell_id, castlevel, formula, duration, res);
 
@@ -2946,9 +2941,6 @@ int Mob::CheckStackConflict(uint16 spellid1, int caster_level1, uint16 spellid2,
 		}
 	}
 
-	int modval = mod_spell_stack(spellid1, caster_level1, caster1, spellid2, caster_level2, caster2);
-	if(modval < 2) { return(modval); }
-
 	/*
 	One of these is a bard song and one isn't and they're both beneficial so they should stack.
 	*/
@@ -3697,8 +3689,6 @@ bool Mob::SpellOnTarget(
 		}
 	}
 
-	mod_spell_cast(spell_id, spelltar, reflect_effectiveness, use_resist_adjust, resist_adjust, isproc);
-
 	if (!DoCastingChecksOnTarget(false, spell_id, spelltar)) {
 		safe_delete(action_packet);
 		return false;
@@ -5067,8 +5057,6 @@ float Mob::ResistSpell(uint8 resist_type, uint16 spell_id, Mob *caster, bool use
 	resist_chance += resist_modifier;
 	resist_chance += target_resist;
 
-	resist_chance = mod_spell_resist(resist_chance, level_mod, resist_modifier, target_resist, resist_type, spell_id, caster);
-
 	//Do our min and max resist checks.
 	if(resist_chance > spells[spell_id].max_resist && spells[spell_id].max_resist != 0)
 	{