poppler: again downgrade the old version

poppler_0_18 can be removed per-package when they're upgraded

pkgs/development/libraries/poppler/0.18.nix

@@ -6,11 +6,11 @@
 }:
 
 stdenv.mkDerivation rec {
-  name = "poppler-0.20.5";
+  name = "poppler-0.18.4";
 
   src = fetchurl {
     url = "${meta.homepage}${name}.tar.gz";
-    sha256 = "1djl0jbgz7m8kbg7sq0wklnlfav5vp7iplkryphvs781by509my6";
+    sha256 = "0bnl05al7mjndp2h0355946j59nfw76f5v0x57d47q68rm412hik";
   };
 
   propagatedBuildInputs = with xorg;

pkgs/top-level/all-packages.nix

@@ -4810,7 +4810,7 @@ let
     gtkSupport = true;
     qt4Support = false;
   };
-  poppler_0_20 = callPackage ../development/libraries/poppler/0.20.nix {
+  poppler_0_18 = callPackage ../development/libraries/poppler/0.18.nix {
     gtkSupport = true;
     qt4Support = false;
   };
@@ -4819,10 +4819,6 @@ let
     gtkSupport = false;
     qt4Support = true;
   };
-  popplerQt4_0_20 = poppler_0_20.override {
-    gtkSupport = false;
-    qt4Support = true;
-  };
 
   popt = callPackage ../development/libraries/popt { };
 
@@ -6724,9 +6720,7 @@ let
       inherit (gnome) libglade;
   };
 
-  calibre = callPackage ../applications/misc/calibre {
-    popplerQt4 = popplerQt4_0_20;
-  };
+  calibre = callPackage ../applications/misc/calibre { };
 
   carrier = builderDefsPackage (import ../applications/networking/instant-messengers/carrier/2.5.0.nix) {
     inherit fetchurl stdenv pkgconfig perl perlXMLParser libxml2 openssl nss
@@ -7034,7 +7028,7 @@ let
   evince = hiPrio (callPackage ../applications/misc/evince {
     inherit (gnome) gnomedocutils gnomeicontheme libgnome
       libgnomeui libglade scrollkeeper;
-    poppler = poppler_0_20;
+    poppler = poppler_0_18;
   });
 
   evolution_data_server = newScope (gnome) ../servers/evolution-data-server { };
@@ -7440,7 +7434,7 @@ let
         freefont_ttf xorg.fontmiscmisc xorg.fontbhttf
       ];
     };
-    poppler = poppler_0_20;
+    poppler = poppler_0_18;
   };
 
   lingot = callPackage ../applications/audio/lingot {