"list --simple-output" should be quiet when there are no packages to list
"list --simple-output" should be quiet when there are no packages to list

Previously:

$ ghc-pkg list --user --simple-output
ghc-pkg: no matches
$

Now:

$ ghc-pkg list --user --simple-output
$

da-x/ghc,forked-upstream-packages-for-ghcjs/ghc,ghc-android/ghc,sgillespie/ghc,mfine/ghc,urbanslug/ghc,mettekou/ghc,elieux/ghc,forked-upstream-packages-for-ghcjs/ghc,mcmaniac/ghc,green-haskell/ghc,vTurbine/ghc,gridaphobe/ghc,lukexi/ghc-7.8-arm64,vikraman/ghc,bitemyapp/ghc,urbanslug/ghc,vikraman/ghc,christiaanb/ghc,olsner/ghc,hferreiro/replay,vikraman/ghc,tjakway/ghcjvm,siddhanathan/ghc,vTurbine/ghc,jstolarek/ghc,lukexi/ghc-7.8-arm64,snoyberg/ghc,ezyang/ghc,mcschroeder/ghc,AlexanderPankiv/ghc,nathyong/microghc-ghc,ezyang/ghc,mcschroeder/ghc,tibbe/ghc,nomeata/ghc,nushio3/ghc,tibbe/ghc,wxwxwwxxx/ghc,lukexi/ghc,forked-upstream-packages-for-ghcjs/ghc,snoyberg/ghc,mcschroeder/ghc,shlevy/ghc,mfine/ghc,shlevy/ghc,ilyasergey/GHC-XAppFix,acowley/ghc,vTurbine/ghc,TomMD/ghc,ezyang/ghc,forked-upstream-packages-for-ghcjs/ghc,nkaretnikov/ghc,nkaretnikov/ghc,tibbe/ghc,forked-upstream-packages-for-ghcjs/ghc,olsner/ghc,christiaanb/ghc,da-x/ghc,bitemyapp/ghc,christiaanb/ghc,gridaphobe/ghc,vTurbine/ghc,siddhanathan/ghc,green-haskell/ghc,shlevy/ghc,hferreiro/replay,GaloisInc/halvm-ghc,anton-dessiatov/ghc,tibbe/ghc,ghc-android/ghc,nathyong/microghc-ghc,nathyong/microghc-ghc,nomeata/ghc,acowley/ghc,ml9951/ghc,hferreiro/replay,ezyang/ghc,fmthoma/ghc,ml9951/ghc,mettekou/ghc,snoyberg/ghc,vTurbine/ghc,sgillespie/ghc,tjakway/ghcjvm,nomeata/ghc,sdiehl/ghc,mcschroeder/ghc,nathyong/microghc-ghc,da-x/ghc,bitemyapp/ghc,gcampax/ghc,TomMD/ghc,jstolarek/ghc,ekmett/ghc,gcampax/ghc,mcmaniac/ghc,nkaretnikov/ghc,spacekitteh/smcghc,green-haskell/ghc,forked-upstream-packages-for-ghcjs/ghc,elieux/ghc,mcmaniac/ghc,acowley/ghc,hferreiro/replay,lukexi/ghc-7.8-arm64,mcmaniac/ghc,wxwxwwxxx/ghc,vikraman/ghc,olsner/ghc,ml9951/ghc,elieux/ghc,sgillespie/ghc,AlexanderPankiv/ghc,lukexi/ghc,nushio3/ghc,nathyong/microghc-ghc,lukexi/ghc,ekmett/ghc,ml9951/ghc,lukexi/ghc-7.8-arm64,olsner/ghc,vikraman/ghc,tjakway/ghcjvm,ilyasergey/GHC-XAppFix,gridaphobe/ghc,urbanslug/ghc,ghc-android/ghc,vTurbine/ghc,sgillespie/ghc,ghc-android/ghc,holzensp/ghc,oldmanmike/ghc,lukexi/ghc,AlexanderPankiv/ghc,sdiehl/ghc,green-haskell/ghc,ezyang/ghc,gcampax/ghc,shlevy/ghc,tjakway/ghcjvm,GaloisInc/halvm-ghc,mettekou/ghc,frantisekfarka/ghc-dsi,mfine/ghc,ml9951/ghc,mcmaniac/ghc,oldmanmike/ghc,ezyang/ghc,mfine/ghc,fmthoma/ghc,sdiehl/ghc,acowley/ghc,ryantm/ghc,snoyberg/ghc,tjakway/ghcjvm,oldmanmike/ghc,nushio3/ghc,sgillespie/ghc,green-haskell/ghc,wxwxwwxxx/ghc,hferreiro/replay,oldmanmike/ghc,gcampax/ghc,sgillespie/ghc,mfine/ghc,elieux/ghc,spacekitteh/smcghc,siddhanathan/ghc,hferreiro/replay,mcschroeder/ghc,acowley/ghc,spacekitteh/smcghc,mettekou/ghc,anton-dessiatov/ghc,ryantm/ghc,nushio3/ghc,ryantm/ghc,tjakway/ghcjvm,da-x/ghc,mfine/ghc,GaloisInc/halvm-ghc,frantisekfarka/ghc-dsi,sdiehl/ghc,snoyberg/ghc,acowley/ghc,nushio3/ghc,snoyberg/ghc,spacekitteh/smcghc,wxwxwwxxx/ghc,frantisekfarka/ghc-dsi,GaloisInc/halvm-ghc,sdiehl/ghc,oldmanmike/ghc,oldmanmike/ghc,holzensp/ghc,ekmett/ghc,wxwxwwxxx/ghc,fmthoma/ghc,AlexanderPankiv/ghc,TomMD/ghc,sdiehl/ghc,jstolarek/ghc,nushio3/ghc,da-x/ghc,urbanslug/ghc,mettekou/ghc,wxwxwwxxx/ghc,olsner/ghc,TomMD/ghc,ilyasergey/GHC-XAppFix,olsner/ghc,olsner/ghc,spacekitteh/smcghc,ryantm/ghc,anton-dessiatov/ghc,bitemyapp/ghc,siddhanathan/ghc,vTurbine/ghc,gcampax/ghc,ml9951/ghc,holzensp/ghc,holzensp/ghc,mcschroeder/ghc,christiaanb/ghc,mfine/ghc,vikraman/ghc,sdiehl/ghc,urbanslug/ghc,nomeata/ghc,gcampax/ghc,ml9951/ghc,TomMD/ghc,elieux/ghc,gridaphobe/ghc,snoyberg/ghc,christiaanb/ghc,nathyong/microghc-ghc,anton-dessiatov/ghc,ryantm/ghc,nkaretnikov/ghc,ghc-android/ghc,elieux/ghc,ilyasergey/GHC-XAppFix,bitemyapp/ghc,nkaretnikov/ghc,AlexanderPankiv/ghc,urbanslug/ghc,elieux/ghc,frantisekfarka/ghc-dsi,shlevy/ghc,lukexi/ghc-7.8-arm64,GaloisInc/halvm-ghc,hferreiro/replay,fmthoma/ghc,fmthoma/ghc,siddhanathan/ghc,christiaanb/ghc,tjakway/ghcjvm,TomMD/ghc,fmthoma/ghc,frantisekfarka/ghc-dsi,shlevy/ghc,forked-upstream-packages-for-ghcjs/ghc,nkaretnikov/ghc,mettekou/ghc,ezyang/ghc,oldmanmike/ghc,lukexi/ghc,vikraman/ghc,anton-dessiatov/ghc,urbanslug/ghc,AlexanderPankiv/ghc,mettekou/ghc,GaloisInc/halvm-ghc,sgillespie/ghc,ghc-android/ghc,jstolarek/ghc,gridaphobe/ghc,GaloisInc/halvm-ghc,ekmett/ghc,gcampax/ghc,nushio3/ghc,christiaanb/ghc,nkaretnikov/ghc,ghc-android/ghc,nathyong/microghc-ghc,TomMD/ghc,siddhanathan/ghc,anton-dessiatov/ghc,acowley/ghc,gridaphobe/ghc,nomeata/ghc,da-x/ghc,shlevy/ghc,AlexanderPankiv/ghc,wxwxwwxxx/ghc,tibbe/ghc,gridaphobe/ghc,da-x/ghc,siddhanathan/ghc,holzensp/ghc,ekmett/ghc,ml9951/ghc,jstolarek/ghc,anton-dessiatov/ghc,fmthoma/ghc,mcschroeder/ghc