[refactor](remove unused code) Remove unused mempool declare or function params (#16222)

* Remove unused mempool declare or function params

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Co-authored-by: yiguolei <yiguolei@gmail.com>

be/src/olap/push_handler.cpp

@@ -320,7 +320,6 @@ Status PushBrokerReader::init(const Schema* schema, const TBrokerScanRange& t_sc
     }
     _runtime_profile = _runtime_state->runtime_profile();
     _runtime_profile->set_name("PushBrokerReader");
-    _tuple_buffer_pool.reset(new MemPool());
 
     _counter.reset(new ScannerCounter());