Adjust DeepSeq to Haskell class/instance syntax.
Adjust DeepSeq to Haskell class/instance syntax.

Adjusted `NFData` instances of `DeepSeq` to syntax changes introduced in
"Implement Haskell class/instance syntax".
See <https://github.com/Frege/frege/pull/193> for more details.

vsts/frege,vsts/frege,vsts/frege