Its no longer used. It seems data from SkillLineAbilitty.dbc is being used instead.
If you want to just add some spells players are going to know, set:
PlayerStart.AllSpells = 1
In worldserver.conf, and then use playercreateinfo_spell_custom table (which will start being used by setting that variable I mentioned to 1).
If you want to remove some spells from list of spells players get when their characters are logged in, try editing DBC I mentioned earlier.:
https://wowdev.wiki/DB/SkillLineAbilityPay attention to field #10: acquireMethod. Spells with on log in learn should have value 2 there. Set it to 0 if you want players to not have some particular spell in that spell's row. Note that spell's ID is in field #3, not in field #1.
