Add cobbled deepslate to default throwaway blocks

[maxsupermanhd]

Describe your suggestion

Well, because it is just like stone.

Final checklist

• I know how to properly use check boxes
• I have not used any OwO's or UwU's in this issue.

[SamchenUF]

Would I be able to work on this?

[rycbar0]

sure if you want to.
just add the line Blocks.COBBLED_DEEPSLATE.asItem(), here

[ZacSharp]

Deepslate should probably be added as well (because stone is already there).

[jake-brennan714]

#4260 closes this (I was looking into doing it but saw this PR)