Revert "fontconfig: fix etc priority"

This reverts commit 1e53d4a777.

Closes #16983

cc @vcunat @ericsagnes @dezgeg

pkgs/development/libraries/fontconfig/default.nix

@@ -68,6 +68,7 @@ stdenv.mkDerivation rec {
     cd "$out/etc/fonts"
     rm conf.d/{50-user,51-local}.conf
     "${libxslt.bin}/bin/xsltproc" --stringparam fontDirectories "${fontbhttf}" \
+      --stringparam fontconfig "$out" \
       --stringparam fontconfigConfigVersion "${configVersion}" \
       --path $out/share/xml/fontconfig \
       ${./make-fonts-conf.xsl} $out/etc/fonts/fonts.conf \

pkgs/development/libraries/fontconfig/make-fonts-conf.xsl

@@ -28,6 +28,8 @@
       <!-- /var/cache/fontconfig is useful for non-nixos systems -->
       <cachedir>/var/cache/fontconfig</cachedir>
 
+      <!-- fontconfig distribution conf.d -->
+      <include><xsl:value-of select="$fontconfig" />/etc/fonts/conf.d</include>
       <!-- versioned system-wide config -->
       <include ignore_missing="yes">/etc/fonts/<xsl:value-of select="$fontconfigConfigVersion" />/conf.d</include>