DBImpl::MultiGet: delete unused var `superversions_to_delete` (#11395)

Summary:
In db_impl.cc DBImpl::MultiGet: delete unused var `superversions_to_delete`

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11395

Reviewed By: ajkr

Differential Revision: D45240896

Pulled By: cbi42

fbshipit-source-id: 0fff99b0d794b6f6d4aadee6036bddd6cb19eb31

db/db_impl/db_impl.cc

@@ -2475,7 +2475,6 @@ std::vector<Status> DBImpl::MultiGet(
 
   // Post processing (decrement reference counts and record statistics)
   PERF_TIMER_GUARD(get_post_process_time);
-  autovector<SuperVersion*> superversions_to_delete;
 
   for (auto mgd_iter : multiget_cf_data) {
     auto mgd = mgd_iter.second;