Remove some missed deprecations

[ZestyBlaze]

Some of the deprecations were missed in the port to 1.21.2(.3), the two I have removed are #c:slimeballs in favour of the new #c:slime_balls and the old DeferredRegister.createDataComponents(String) initalizer as we have the new much more favourable method. Both of these are things that were marked to be removed in 1.21.2 and were not.
I did ask about things to remove and another developer mentioned the other createDataComponents as it would make better sense for us to get it out as it was only used for a short period of time and the alternate option is a much better option.
I also previously looked at removing the fallbacks for the Oxidising and Waxing datamaps which are marked to be removed in 1.21.2 but have not been, however another maintainer said to leave them until 1.22
Another possible removal could be IEntityExtension.serializeNBT as this is marked to be removed too and hasn't yet as it doesn't specify a removal period

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

[neoforged-compatibility-checks]

@ZestyBlaze, this PR introduces breaking changes.
Fortunately, this project is currently accepting breaking changes, but if they are not intentional, please revert them.
Last checked commit: 4ae1445091b78625da7b78ede34615a467fa7bb3.

neoforge (:neoforge)

• net/neoforged/neoforge/registries/DeferredRegister$DataComponents
  • <init>(Ljava/lang/String;)V: ❗ API method was removed
• net/neoforged/neoforge/common/Tags$Items
  • SLIMEBALLS:Lnet/minecraft/tags/TagKey;: ❗ API field was removed
• net/neoforged/neoforge/registries/DeferredRegister
  • createDataComponents(Ljava/lang/String;)Lnet/neoforged/neoforge/registries/DeferredRegister$DataComponents;: ❗ API method was removed