kde4: unify used libcanberra

I wondered why I'm getting two versions in the closure of KDE apps.

pkgs/desktops/kde-4.10/kde-runtime.nix

···
 , networkmanager, kactivities, kdepimlibs, openexr, ilmbase, config
 }:
 
-let libcanberraWithoutGTK = if (config ? kde_runtime && config.kde_runtime ? libcanberraWithoutGTK)
-                            then config.kde_runtime.libcanberraWithoutGTK
-                            else true;
-
-    canberra = if libcanberraWithoutGTK
-               then libcanberra.override { gtk = null; }
-               else libcanberra;
-in
-
 kde {
   buildInputs = [
     kdelibs attica xz bzip2 libssh libjpeg exiv2 ntrack
-    qca2 samba canberra pulseaudio
+    qca2 samba libcanberra pulseaudio
     networkmanager kactivities kdepimlibs openexr
 #todo: add openslp
   ];

pkgs/desktops/kde-4.7/kde-runtime.nix

···
 kde {
   buildInputs =
     [ kdelibs shared_desktop_ontologies bzip2 libssh exiv2 attica
-      samba (libcanberra.override { gtk = null; }) ntrack libjpeg
+      samba libcanberra ntrack libjpeg
     ];
 
   passthru.propagatedUserEnvPackages = [ virtuoso ];

pkgs/desktops/kde-4.8/kde-runtime.nix

···
 kde {
   buildInputs =
     [ kdelibs shared_desktop_ontologies bzip2 libssh exiv2 attica xz networkmanager
-      samba (libcanberra.override { gtk = null; }) ntrack libjpeg qca2 pulseaudio
+      samba libcanberra ntrack libjpeg qca2 pulseaudio
     ];
 
   nativeBuildInputs = [ pkgconfig ];

pkgs/top-level/all-packages.nix

···
   libcaca = callPackage ../development/libraries/libcaca { };
 
   libcanberra = callPackage ../development/libraries/libcanberra { };
+  libcanberra_kde = if (config.kde_runtime.libcanberraWithoutGTK or true)
+    then libcanberra.override { gtk = null; }
+    else libcanberra;
 
   libcello = callPackage ../development/libraries/libcello {};
 
···
       eigen = eigen2;
       libotr = libotr_3_2;
       libgphoto2 = libgphoto2_4;
+      libcanberra = libcanberra_kde;
     }) ../desktops/kde-4.7;
 
   kde48 = kdePackagesFor (pkgs.kde48 // {
···
       eigen = eigen2;
       libotr = libotr_3_2;
       libgphoto2 = libgphoto2_4;
+      libcanberra = libcanberra_kde;
     }) ../desktops/kde-4.8;
 
   kde410 = kdePackagesFor (pkgs.kde410 // {
···
       libotr = libotr_3_2;
       libusb = libusb1;
       ffmpeg = ffmpeg_1;
+      libcanberra = libcanberra_kde;
     }) ../desktops/kde-4.10;
 
   kdePackagesFor = self: dir: