libutil: Move references.{hh,cc} to libstore

The implicit dependency on refLength (which is the StorePath::HashLen)
is not good. Also the companion tests and benchmarks are already in libstore-tests.

src/libutil-tests/meson.build

@@ -66,7 +66,6 @@ sources = files(
   'pool.cc',
   'position.cc',
   'processes.cc',
-  'references.cc',
   'sort.cc',
   'spawn.cc',
   'strings.cc',

src/libutil-tests/references.cc

@@ -1,45 +0,0 @@
-#include "nix/util/references.hh"
-#include <gtest/gtest.h>
-
-namespace nix {
-
-using std::string;
-
-struct RewriteParams
-{
-    string originalString, finalString;
-    StringMap rewrites;
-
-    friend std::ostream & operator<<(std::ostream & os, const RewriteParams & bar)
-    {
-        StringSet strRewrites;
-        for (auto & [from, to] : bar.rewrites)
-            strRewrites.insert(from + "->" + to);
-        return os << "OriginalString: " << bar.originalString << std::endl
-                  << "Rewrites: " << dropEmptyInitThenConcatStringsSep(",", strRewrites) << std::endl
-                  << "Expected result: " << bar.finalString;
-    }
-};
-
-class RewriteTest : public ::testing::TestWithParam<RewriteParams>
-{};
-
-TEST_P(RewriteTest, IdentityRewriteIsIdentity)
-{
-    RewriteParams param = GetParam();
-    StringSink rewritten;
-    auto rewriter = RewritingSink(param.rewrites, rewritten);
-    rewriter(param.originalString);
-    rewriter.flush();
-    ASSERT_EQ(rewritten.s, param.finalString);
-}
-
-INSTANTIATE_TEST_CASE_P(
-    references,
-    RewriteTest,
-    ::testing::Values(
-        RewriteParams{"foooo", "baroo", {{"foo", "bar"}, {"bar", "baz"}}},
-        RewriteParams{"foooo", "bazoo", {{"fou", "bar"}, {"foo", "baz"}}},
-        RewriteParams{"foooo", "foooo", {}}));
-
-} // namespace nix