Two small compiler warning fixes

plugins/producer_plugin/producer_plugin.cpp

@@ -1584,8 +1584,6 @@ void producer_plugin_impl::produce_block() {
    } );
 
    chain.commit_block();
-   auto hbt = chain.head_block_time();
-   //idump((fc::time_point::now() - hbt));
 
    block_state_ptr new_bs = chain.head_block_state();
    _producer_watermarks[new_bs->header.producer] = chain.head_block_num();

plugins/txn_test_gen_plugin/txn_test_gen_plugin.cpp

@@ -436,7 +436,7 @@ void txn_test_gen_plugin::plugin_shutdown() {
    try {
       my->stop_generation();
    }
-   catch(fc::exception e) {
+   catch(fc::exception& e) {
    }
 }