refactor(3p/nix): Replace tokenizeStrings with absl::StrSplit

This function was a custom (and inefficient in the case of
single-character delimiters) string splitter which was used all over
the codebase. Abseil provides an appropriate replacement function.

third_party/nix/src/nix-daemon/nix-daemon.cc

@@ -526,7 +526,7 @@ static void performOp(TunnelLogger* logger, const ref<Store>& store,
             trusted.insert(s);
           }
           Strings subs;
-          auto ss = tokenizeString<Strings>(value);
+          Strings ss = absl::StrSplit(value, absl::ByAnyChar(" \t\n\r"));
           for (auto& s : ss) {
             if (trusted.count(s) != 0u) {
               subs.push_back(s);