TcDeriv: Use a NameEnv instead of association list
TcDeriv: Use a NameEnv instead of association list

It's unlikely that these lists would have become very large but
nevertheless this is an easy and worthwhile change.

Reviewed By: austin

Differential Revision: https://phabricator.haskell.org/D1265

snoyberg/ghc,mcschroeder/ghc,GaloisInc/halvm-ghc,sgillespie/ghc,sgillespie/ghc,mettekou/ghc,nushio3/ghc,GaloisInc/halvm-ghc,snoyberg/ghc,ml9951/ghc,ml9951/ghc,vTurbine/ghc,olsner/ghc,oldmanmike/ghc,vikraman/ghc,AlexanderPankiv/ghc,vikraman/ghc,sdiehl/ghc,tjakway/ghcjvm,elieux/ghc,ezyang/ghc,siddhanathan/ghc,elieux/ghc,gridaphobe/ghc,oldmanmike/ghc,da-x/ghc,AlexanderPankiv/ghc,snoyberg/ghc,shlevy/ghc,sdiehl/ghc,vikraman/ghc,oldmanmike/ghc,mettekou/ghc,mcschroeder/ghc,mettekou/ghc,ghc-android/ghc,nushio3/ghc,AlexanderPankiv/ghc,sgillespie/ghc,tjakway/ghcjvm,nushio3/ghc,ghc-android/ghc,sgillespie/ghc,nushio3/ghc,da-x/ghc,shlevy/ghc,da-x/ghc,snoyberg/ghc,shlevy/ghc,mettekou/ghc,GaloisInc/halvm-ghc,ezyang/ghc,snoyberg/ghc,shlevy/ghc,sgillespie/ghc,tjakway/ghcjvm,vTurbine/ghc,ml9951/ghc,siddhanathan/ghc,siddhanathan/ghc,ml9951/ghc,AlexanderPankiv/ghc,elieux/ghc,da-x/ghc,tjakway/ghcjvm,nushio3/ghc,mettekou/ghc,ghc-android/ghc,ghc-android/ghc,vikraman/ghc,ml9951/ghc,ezyang/ghc,sgillespie/ghc,mcschroeder/ghc,sdiehl/ghc,mcschroeder/ghc,gridaphobe/ghc,shlevy/ghc,ml9951/ghc,da-x/ghc,sdiehl/ghc,da-x/ghc,shlevy/ghc,vTurbine/ghc,elieux/ghc,mcschroeder/ghc,olsner/ghc,olsner/ghc,AlexanderPankiv/ghc,vTurbine/ghc,AlexanderPankiv/ghc,tjakway/ghcjvm,sdiehl/ghc,elieux/ghc,vikraman/ghc,vikraman/ghc,GaloisInc/halvm-ghc,siddhanathan/ghc,ezyang/ghc,ezyang/ghc,nushio3/ghc,elieux/ghc,oldmanmike/ghc,ezyang/ghc,shlevy/ghc,GaloisInc/halvm-ghc,ml9951/ghc,siddhanathan/ghc,oldmanmike/ghc,ezyang/ghc,ghc-android/ghc,olsner/ghc,sdiehl/ghc,siddhanathan/ghc,gridaphobe/ghc,siddhanathan/ghc,gridaphobe/ghc,vTurbine/ghc,oldmanmike/ghc,oldmanmike/ghc,tjakway/ghcjvm,AlexanderPankiv/ghc,gridaphobe/ghc,mettekou/ghc,snoyberg/ghc,olsner/ghc,mettekou/ghc,vTurbine/ghc,vikraman/ghc,mcschroeder/ghc,ghc-android/ghc,da-x/ghc,snoyberg/ghc,sdiehl/ghc,GaloisInc/halvm-ghc,vTurbine/ghc,gridaphobe/ghc,mcschroeder/ghc,gridaphobe/ghc,elieux/ghc,nushio3/ghc,olsner/ghc,sgillespie/ghc,ml9951/ghc,ghc-android/ghc,tjakway/ghcjvm,olsner/ghc,GaloisInc/halvm-ghc