removed listener closing in gracefully shutdown json-rpc server

[valli0x]

we don't need to close listener when call server.Shutdown, otherwise we will get an error

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 46.17%. Comparing base (8afdc69) to head (1ab6df3).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
server/json_rpc.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #550   +/-   ##
========================================
  Coverage    46.17%   46.17%           
========================================
  Files          181      181           
  Lines        18124    18124           
========================================
  Hits          8368     8368           
  Misses        9039     9039           
  Partials       717      717           

Files with missing lines	Coverage Δ
server/json_rpc.go	0.00% <0.00%> (ø)