Always load totalEntityAge

[Rothes]

This variable totalEntityAge seems always being saved, but only loads if entity is LivingEntity.

I believe there was a reason not to load it when it was tickCount, but since we have separated that, I don't see a reason why we don't load it anytime.

despawnTime could behave better on some projectiles (like wither skull) after this.

[Lulu13022002]

It seems to have been done kinda on purpose in #12077 (comment) to not break the API, now this is indeed weird for the config value.
Also this is added code by us so can just remove the if statement here.

[Rothes]

If statement is now removed.

I think we could keep the old API behavior.
bukkitEntity.getTicksLived now returns totalEntityAge , we can make it returns tickCount for non-LivingEntity.

However, I think a better approach, is to add new API, so dev can get both tickCount and totalEntityAge.
One for total age; One for ticked times since it's loaded.

( tickCount is also stored in some entities (AreaEffectCloud), so it will always return same value with totalEntityAge )