Remvoe unnecessary deferal of server close

[pancak3]

The last line is produced by the unnecessary code

I0824 07:06:34.181777   85035 simulator.go:201] "HTTP server starting"
I0824 07:06:40.699245   85035 simulator.go:396] "reqProcessingWorker stopped:" worker id=2
I0824 07:06:40.699368   85035 simulator.go:208] "Shutdown signal received, shutting down HTTP server gracefully"
I0824 07:06:40.701089   85035 simulator.go:396] "reqProcessingWorker stopped:" worker id=5
I0824 07:06:40.699663   85035 simulator.go:396] "reqProcessingWorker stopped:" worker id=3
I0824 07:06:40.699605   85035 simulator.go:396] "reqProcessingWorker stopped:" worker id=1
I0824 07:06:40.699596   85035 simulator.go:396] "reqProcessingWorker stopped:" worker id=4
I0824 07:06:40.705896   85035 simulator.go:216] "HTTP server stopped"
E0824 07:06:40.708202   85035 simulator.go:194] "server listener close failed" err="close tcp4 0.0.0.0:8000: use of closed network connection"

[irar2]

server.Shutdown() closes all the listeners

/lgtm
/approve