treewide: use dontUnpack

pkgs/data/fonts/migmix/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation rec {
     })
   ];
 
-  unpackPhase = ":";
+  dontUnpack = true;
 
   installPhase = ''
     find $srcs -name '*.ttf' -exec install -m644 -Dt $out/share/fonts/truetype/migmix {} \;

pkgs/data/fonts/migu/default.nix

@@ -23,7 +23,7 @@ stdenv.mkDerivation rec {
     })
   ];
 
-  unpackPhase = ":";
+  dontUnpack = true;
 
   installPhase = ''
     find $srcs -name '*.ttf' | xargs install -m644 --target $out/share/fonts/truetype/migu -D

pkgs/data/fonts/poly/default.nix

@@ -19,7 +19,7 @@ stdenv.mkDerivation rec {
 
   sourceRoot = ".";
 
-  unpackPhase = "true";
+  dontUnpack = true;
 
   installPhase = ''
     mkdir -p $out/share/fonts/opentype

pkgs/data/misc/nixos-artwork/wallpapers.nix

@@ -6,7 +6,7 @@ let
     stdenv.mkDerivation {
       inherit name src;
 
-      unpackPhase = "true";
+      dontUnpack = true;
 
       installPhase = ''
         mkdir -p $out/share/artwork/gnome

pkgs/data/sgml+xml/schemas/sgml-dtd/docbook/3.1.nix

@@ -17,7 +17,7 @@ in
 stdenv.mkDerivation {
   name = "docbook-sgml-3.1";
 
-  unpackPhase = "true";
+  dontUnpack = true;
 
   nativeBuildInputs = [ unzip ];
 

pkgs/data/sgml+xml/schemas/sgml-dtd/docbook/4.1.nix

@@ -17,7 +17,7 @@ in
 stdenv.mkDerivation {
   name = "docbook-sgml-4.1";
 
-  unpackPhase = "true";
+  dontUnpack = true;
 
   nativeBuildInputs = [ unzip ];