Remove 'accessor' from addToStore()

This is only used by hydra-queue-runner and it's better to implement
it there.

src/libstore/binary-cache-store.hh

@@ -79,8 +79,7 @@ public:
     { unsupported("queryPathFromHashPart"); }
 
     void addToStore(const ValidPathInfo & info, Source & narSource,
-        RepairFlag repair, CheckSigsFlag checkSigs,
-        std::shared_ptr<FSAccessor> accessor) override;
+        RepairFlag repair, CheckSigsFlag checkSigs) override;
 
     StorePath addToStore(const string & name, const Path & srcPath,
         FileIngestionMethod method, HashType hashAlgo,