treewide: pkgs/**.nix: remove trailing whitespaces

Manually remove trailing white spaces
in `pkgs/**.nix` with the help of an editor

Auto-generated nix expressions containing trailing whitespaces:

*   pkgs/development/haskell-modules/hackage-packages.nix
    *   See issue https://github.com/NixOS/cabal2nix/issues/208
*   pkgs/**/eggs.nix
    *   I don't know how they are generated,
        but they seems to be Python-related.

pkgs/build-support/upstream-updater/attrset-to-dir.nix

@@ -2,7 +2,6 @@ a :
 a.stdenv.mkDerivation {
   buildCommand = ''
     mkdir -p "$out/attributes"
-    
   '' + (a.lib.concatStrings (map
     (n: ''
       ln -s "${a.writeTextFile {name=n; text=builtins.getAttr n a.theAttrSet;}}" $out/attributes/${n};

pkgs/top-level/emscripten-packages.nix

@@ -127,7 +127,6 @@ rec {
       cp README.md $doc/share/${pname}
     '';
     checkPhase = ''
-      
     '';
   };