[Dubbo-4479]Delete unused code. defaultPort can not be null. #4479

[TingSky]

What is the purpose of the change

Delete unused code

Verifying this change

First PR

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[codecov-io]

Codecov Report

Merging #4480 into master will increase coverage by 0.63%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #4480      +/-   ##
============================================
+ Coverage     62.34%   62.98%   +0.63%     
  Complexity      450      450              
============================================
  Files           791      770      -21     
  Lines         34852    33005    -1847     
  Branches       5457     5216     -241     
============================================
- Hits          21730    20789     -941     
+ Misses        10624     9823     -801     
+ Partials       2498     2393     -105

Impacted Files	Coverage Δ	Complexity Δ
...in/java/org/apache/dubbo/config/ServiceConfig.java	58.42% <100%> (+0.21%)	0 <0> (ø)	⬇️
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0%> (-8.7%)	0% <0%> (ø)
...ng/exchange/support/header/HeartbeatTimerTask.java	73.68% <0%> (-5.27%)	0% <0%> (ø)
...bo/rpc/cluster/support/FailbackClusterInvoker.java	67.21% <0%> (-3.28%)	0% <0%> (ø)
...a/org/apache/dubbo/common/json/ParseException.java
...o/rpc/protocol/thrift/DubboClassNameGenerator.java
.../java/org/apache/dubbo/common/json/JSONObject.java
.../java/org/apache/dubbo/common/json/JSONWriter.java
.../apache/dubbo/rpc/protocol/thrift/ThriftUtils.java
.../java/org/apache/dubbo/common/json/JSONReader.java
... and 20 more

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[CrazyHZM]

LGTM