[optimize]Refactor the dubbo-demo module

[heliang666s]

What is the purpose of the change?

1. Remove dubbo-demo-xml, dubbo-demo-annotation, dubbo-demo-generic-call and dubbo-demo-interface.
2. Change all default protocols from dubbo to triple.
3. Update README.md.

Checklist

• Make sure there is a GitHub_issue field for the change.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Make sure gitHub actions can pass. Why the workflow is failing and how to fix it?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.19%. Comparing base (ef6e8bd) to head (0261a18).
Report is 55 commits behind head on 3.3.

❗ Current head 0261a18 differs from pull request most recent head 2af91b4

Please upload reports for the commit 2af91b4 to get more accurate results.

Additional details and impacted files

@@              Coverage Diff              @@
##              3.3    #14871        +/-   ##
=============================================
- Coverage   37.53%     2.19%    -35.34%     
=============================================
  Files        1813     26083     +24270     
  Lines       80737   1389674   +1308937     
  Branches    12005    220210    +208205     
=============================================
+ Hits        30304     30566       +262     
- Misses      46042   1354670   +1308628     
- Partials     4391      4438        +47     

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[CrazyHZM]

Currently, it cannot be deleted, and the native ci test relies on it.

[AlbumenJ]