partition_version: remove _schema from partition_entry::operator<<

operator<< accepts a schema& and a partition_entry&. But since the latter
now contains a reference to its schema inside, the former is redundant.
Remove it.

row_cache.cc

@@ -1369,6 +1369,6 @@ std::ostream& operator<<(std::ostream& out, const cache_entry& e) {
     return out << "{cache_entry: " << e.position()
                << ", cont=" << e.continuous()
                << ", dummy=" << e.is_dummy_entry()
-               << ", " << partition_entry::printer(*e.schema(), e.partition())
+               << ", " << partition_entry::printer(e.partition())
                << "}";
 }