Delete unused code.

[ghost]

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• Why submit this pull request?

• Bug fix

• New feature provided

• Improve performance

• Related issues

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Bug fix

• Bug description.

• How to fix?

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New feature or improvement

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[codecov-io]

Codecov Report

Merging #4178 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4178      +/-   ##
==========================================
- Coverage   26.82%   26.77%   -0.05%     
==========================================
  Files        1163     1163              
  Lines       25428    25426       -2     
  Branches     3691     3691              
==========================================
- Hits         6820     6807      -13     
- Misses      18000    18013      +13     
+ Partials      608      606       -2

Impacted Files	Coverage Δ
.../java/org/apache/skywalking/oal/rt/OALRuntime.java	0% <ø> (ø)	⬆️
.../core/remote/ServiceAndEndpointRegisterClient.java	31.46% <0%> (-13.49%)	⬇️
...walking/apm/agent/core/context/TracingContext.java	58.2% <0%> (-0.5%)	⬇️

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[wayilau]

Unused, indeed.