Reduce get_dynamic_global_properties() call
Reduce get_dynamic_global_properties() call

Even though get_slot_time(uint32_t slot) caches the result of get_dynamic_global_properties() on local value, it doesn't use the value properly. The additional get_dynamic_global_properties() call which leads to chainbase search can be removed just not using head_block_num() and head_block_time() in this context.
EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos