[DUBBO-3137]: step3, remove constants completely.

[beiwei30]

What is the purpose of the change

issue #3137: step3, remove constants completely.

Brief changelog

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Verifying this change

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[codecov-io]

Codecov Report

Merging #4053 into master will decrease coverage by 0.01%.
The diff coverage is 73.63%.

@@             Coverage Diff              @@
##             master    #4053      +/-   ##
============================================
- Coverage        63%   62.99%   -0.02%     
- Complexity      543      544       +1     
============================================
  Files           757      756       -1     
  Lines         32570    32569       -1     
  Branches       5162     5162              
============================================
- Hits          20521    20516       -5     
- Misses         9684     9694      +10     
+ Partials       2365     2359       -6

Impacted Files	Coverage Δ	Complexity Δ
.../apache/dubbo/qos/protocol/QosProtocolWrapper.java	64.1% <ø> (-17.95%)	0 <0> (ø)
...onfigcenter/consul/ConsulDynamicConfiguration.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...ain/java/org/apache/dubbo/config/MethodConfig.java	95.12% <ø> (ø)	0 <0> (ø)	⬇️
...enter/support/nacos/NacosDynamicConfiguration.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...g/apache/dubbo/config/AbstractReferenceConfig.java	94% <ø> (ø)	0 <0> (ø)	⬇️
...pache/dubbo/monitor/dubbo/DubboMonitorFactory.java	100% <ø> (ø)	6 <0> (ø)	⬇️
...gcenter/support/etcd/EtcdDynamicConfiguration.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...pport/zookeeper/ZookeeperDynamicConfiguration.java	83.33% <ø> (ø)	6 <0> (ø)	⬇️
...e/dubbo/registry/integration/RegistryProtocol.java	82.69% <ø> (ø)	0 <0> (ø)	⬇️
.../main/java/com/alibaba/dubbo/common/Constants.java	0% <0%> (ø)	0 <0> (ø)	⬇️
... and 36 more

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[CrazyHZM]

Please take a look my comment.

[CrazyHZM]

LGTM

[beiwei30]

so, now we should move to step4, start to review any constants suitable to move back to its own module.