triedb: using testing.B.Loop

[hoanguyenkh]

before
go test -run=^$ -bench=. ./triedb/... -timeout=1h 39.12s user 2.43s system 111% cpu 37.191 total
after
go test -run=^$ -bench=. ./triedb/... -timeout=1h 28.51s user 2.08s system 111% cpu 27.520 total

[rjl493456442]

There is no necessity to switch all benchmarks to b.Loop style.