Remove obsolete `digitsTyConKey :: Unique`
Remove obsolete `digitsTyConKey :: Unique`

This became dead with 1e87c0a6e485e1dbef8e9ed19191e54f6cdc54e0
and was probably just missed.

I plan to re-use the freed up `mkPreludeTyConUnique 23` slot soon
for a new `bigNatTyConKey` (as part of the #9281 effort)

TomMD/ghc,mcschroeder/ghc,ml9951/ghc,oldmanmike/ghc,shlevy/ghc,siddhanathan/ghc,green-haskell/ghc,mcschroeder/ghc,forked-upstream-packages-for-ghcjs/ghc,oldmanmike/ghc,GaloisInc/halvm-ghc,shlevy/ghc,wxwxwwxxx/ghc,ezyang/ghc,fmthoma/ghc,nushio3/ghc,fmthoma/ghc,mfine/ghc,oldmanmike/ghc,christiaanb/ghc,mfine/ghc,da-x/ghc,TomMD/ghc,mettekou/ghc,elieux/ghc,vikraman/ghc,oldmanmike/ghc,snoyberg/ghc,TomMD/ghc,mcschroeder/ghc,da-x/ghc,GaloisInc/halvm-ghc,mettekou/ghc,nushio3/ghc,anton-dessiatov/ghc,siddhanathan/ghc,wxwxwwxxx/ghc,ghc-android/ghc,snoyberg/ghc,jstolarek/ghc,AlexanderPankiv/ghc,urbanslug/ghc,mcschroeder/ghc,tjakway/ghcjvm,ghc-android/ghc,snoyberg/ghc,wxwxwwxxx/ghc,GaloisInc/halvm-ghc,wxwxwwxxx/ghc,nkaretnikov/ghc,spacekitteh/smcghc,christiaanb/ghc,nathyong/microghc-ghc,fmthoma/ghc,gridaphobe/ghc,ghc-android/ghc,da-x/ghc,green-haskell/ghc,snoyberg/ghc,sdiehl/ghc,sgillespie/ghc,nushio3/ghc,olsner/ghc,mettekou/ghc,nathyong/microghc-ghc,TomMD/ghc,olsner/ghc,sdiehl/ghc,GaloisInc/halvm-ghc,tjakway/ghcjvm,olsner/ghc,vTurbine/ghc,da-x/ghc,forked-upstream-packages-for-ghcjs/ghc,AlexanderPankiv/ghc,bitemyapp/ghc,elieux/ghc,fmthoma/ghc,ghc-android/ghc,tjakway/ghcjvm,nkaretnikov/ghc,acowley/ghc,jstolarek/ghc,ghc-android/ghc,ezyang/ghc,sgillespie/ghc,sgillespie/ghc,gridaphobe/ghc,mettekou/ghc,anton-dessiatov/ghc,spacekitteh/smcghc,vTurbine/ghc,spacekitteh/smcghc,shlevy/ghc,gridaphobe/ghc,wxwxwwxxx/ghc,ezyang/ghc,AlexanderPankiv/ghc,sgillespie/ghc,ml9951/ghc,forked-upstream-packages-for-ghcjs/ghc,forked-upstream-packages-for-ghcjs/ghc,fmthoma/ghc,elieux/ghc,tjakway/ghcjvm,jstolarek/ghc,siddhanathan/ghc,acowley/ghc,ghc-android/ghc,anton-dessiatov/ghc,AlexanderPankiv/ghc,nushio3/ghc,vTurbine/ghc,gridaphobe/ghc,nushio3/ghc,sgillespie/ghc,bitemyapp/ghc,ml9951/ghc,snoyberg/ghc,vikraman/ghc,vikraman/ghc,fmthoma/ghc,ezyang/ghc,siddhanathan/ghc,snoyberg/ghc,gcampax/ghc,christiaanb/ghc,urbanslug/ghc,christiaanb/ghc,urbanslug/ghc,nathyong/microghc-ghc,christiaanb/ghc,olsner/ghc,mfine/ghc,forked-upstream-packages-for-ghcjs/ghc,mettekou/ghc,urbanslug/ghc,nathyong/microghc-ghc,vikraman/ghc,olsner/ghc,GaloisInc/halvm-ghc,ml9951/ghc,siddhanathan/ghc,anton-dessiatov/ghc,urbanslug/ghc,shlevy/ghc,mcschroeder/ghc,gcampax/ghc,gcampax/ghc,snoyberg/ghc,sgillespie/ghc,nkaretnikov/ghc,vikraman/ghc,da-x/ghc,ezyang/ghc,shlevy/ghc,urbanslug/ghc,bitemyapp/ghc,fmthoma/ghc,AlexanderPankiv/ghc,nkaretnikov/ghc,TomMD/ghc,forked-upstream-packages-for-ghcjs/ghc,vTurbine/ghc,wxwxwwxxx/ghc,acowley/ghc,AlexanderPankiv/ghc,ghc-android/ghc,vTurbine/ghc,tjakway/ghcjvm,nkaretnikov/ghc,nushio3/ghc,AlexanderPankiv/ghc,ml9951/ghc,spacekitteh/smcghc,sdiehl/ghc,nathyong/microghc-ghc,shlevy/ghc,sgillespie/ghc,tjakway/ghcjvm,gridaphobe/ghc,jstolarek/ghc,christiaanb/ghc,green-haskell/ghc,siddhanathan/ghc,sdiehl/ghc,nathyong/microghc-ghc,oldmanmike/ghc,da-x/ghc,elieux/ghc,elieux/ghc,green-haskell/ghc,ml9951/ghc,gcampax/ghc,jstolarek/ghc,anton-dessiatov/ghc,nkaretnikov/ghc,acowley/ghc,bitemyapp/ghc,spacekitteh/smcghc,elieux/ghc,wxwxwwxxx/ghc,nushio3/ghc,mettekou/ghc,ezyang/ghc,TomMD/ghc,ml9951/ghc,olsner/ghc,urbanslug/ghc,da-x/ghc,vikraman/ghc,GaloisInc/halvm-ghc,elieux/ghc,anton-dessiatov/ghc,tjakway/ghcjvm,acowley/ghc,vTurbine/ghc,GaloisInc/halvm-ghc,gridaphobe/ghc,mfine/ghc,sdiehl/ghc,oldmanmike/ghc,sdiehl/ghc,ezyang/ghc,mfine/ghc,vikraman/ghc,nkaretnikov/ghc,mettekou/ghc,mcschroeder/ghc,green-haskell/ghc,sdiehl/ghc,mfine/ghc,gridaphobe/ghc,siddhanathan/ghc,gcampax/ghc,mcschroeder/ghc,vTurbine/ghc,TomMD/ghc,christiaanb/ghc,oldmanmike/ghc,ml9951/ghc,acowley/ghc,mfine/ghc,forked-upstream-packages-for-ghcjs/ghc,gcampax/ghc,anton-dessiatov/ghc,bitemyapp/ghc,nathyong/microghc-ghc,olsner/ghc,gcampax/ghc,acowley/ghc,shlevy/ghc