Eliminate old TeeSink abstraction

This was introduced in fa125b9b28, and
then "reverted" in 1cf4801108, except that
revert left the struct around doing nothing useful.

We're removing it all the way now because we want to make a new
`TeeSink` complementing the already-exiting `TeeSource`, that is
actually a completely different concept as far as the class hierarchy is
concerned.

src/libstore/daemon.cc

@@ -721,9 +721,10 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         if (GET_PROTOCOL_MINOR(clientVersion) >= 21)
             source = std::make_unique<TunnelSource>(from, to);
         else {
-            TeeSink tee(from);
-            parseDump(tee, tee.source);
-            saved = std::move(*tee.source.data);
+            TeeSource tee(from);
+            ParseSink sink;
+            parseDump(sink, tee);
+            saved = std::move(*tee.data);
             source = std::make_unique<StringSource>(saved);
         }
 

src/libstore/export-import.cc

@@ -77,8 +77,9 @@ StorePaths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> acces
         if (n != 1) throw Error("input doesn't look like something created by 'nix-store --export'");
 
         /* Extract the NAR from the source. */
-        TeeSink tee(source);
-        parseDump(tee, tee.source);
+        TeeSource tee(source);
+        ParseSink sink;
+        parseDump(sink, tee);
 
         uint32_t magic = readInt(source);
         if (magic != exportMagic)
@@ -94,15 +95,15 @@ StorePaths Store::importPaths(Source & source, std::shared_ptr<FSAccessor> acces
         if (deriver != "")
             info.deriver = parseStorePath(deriver);
 
-        info.narHash = hashString(htSHA256, *tee.source.data);
-        info.narSize = tee.source.data->size();
+        info.narHash = hashString(htSHA256, *tee.data);
+        info.narSize = tee.data->size();
 
         // Ignore optional legacy signature.
         if (readInt(source) == 1)
             readString(source);
 
         // Can't use underlying source, which would have been exhausted
-        auto source = StringSource { *tee.source.data };
+        auto source = StringSource { *tee.data };
         addToStore(info, source, NoRepair, checkSigs, accessor);
 
         res.push_back(info.path);

src/libutil/archive.hh

@@ -63,13 +63,6 @@ struct ParseSink
     virtual void createSymlink(const Path & path, const string & target) { };
 };
 
-struct TeeSink : ParseSink
-{
-    TeeSource source;
-
-    TeeSink(Source & source) : source(source) { }
-};
-
 void parseDump(ParseSink & sink, Source & source);
 
 void restorePath(const Path & path, Source & source);