Add removeReferencesTo for removing specific refs

This allows for a less blanket approach than nuke-refs, targetting specific
references that we know we don't want rather than all references that we don't
know we want.

pkgs/build-support/remove-references-to/default.nix

···
+# The program `remove-references-to' created by this derivation replaces all
+# references to the given Nix store paths in the specified files by a
+# non-existent path (/nix/store/eeee...).  This is useful for getting rid of
+# dependencies that you know are not actually needed at runtime.
+
+{ stdenv, writeScriptBin }:
+
+writeScriptBin "remove-references-to" ''
+#! ${stdenv.shell} -e
+
+# References to remove
+targets=()
+while getopts t: o; do
+    case "$o" in
+        t) storeId=$(echo "$OPTARG" | sed -n "s|^$NIX_STORE/\\([a-z0-9]\{32\}\\)-.*|\1|p")
+           if [ -z "$storeId" ]; then
+               echo "-t argument must be a Nix store path"
+               exit 1
+           fi
+           targets+=("$storeId")
+    esac
+done
+shift $(($OPTIND-1))
+
+# Files to remove the references from
+regions=()
+for i in "$@"; do
+    test ! -L "$i" -a -f "$i" && regions+=("$i")
+done
+
+for target in "''${targets[@]}" ; do
+    sed -i -e "s|$NIX_STORE/$target-|$NIX_STORE/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-|g" "''${regions[@]}"
+done
+''

pkgs/top-level/all-packages.nix

···
 
   nukeReferences = callPackage ../build-support/nuke-references/default.nix { };
 
+  removeReferencesTo = callPackage ../build-support/remove-references-to/default.nix { };
+
   vmTools = callPackage ../build-support/vm/default.nix { };
 
   releaseTools = callPackage ../build-support/release/default.nix { };