Remove Kubernetes and xDS implementations

[AlbumenJ]

What is the purpose of the change

Kubernetes and xDS implementations have been moved to dubbo-spi-extensions in apache/dubbo-spi-extensions#251. These two implementations will incubate there in the future.

Brief changelog

Verifying this change

Checklist

• Make sure there is a GitHub_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GitHub issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Check if is necessary to patch to Dubbo 3 if you are work on Dubbo 2.7
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Add some description to dubbo-website project if you are requesting to add a feature.
• GitHub Actions works fine on your own branch.
• If this contribution is large, please follow the Software Donation Guide.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5554706) 69.47% compared to head (d57b4ac) 70.29%.

Additional details and impacted files

@@             Coverage Diff              @@
##                3.2   #13469      +/-   ##
============================================
+ Coverage     69.47%   70.29%   +0.82%     
  Complexity        2        2              
============================================
  Files          1655     1602      -53     
  Lines         71701    69874    -1827     
  Branches      10278    10090     -188     
============================================
- Hits          49812    49121     -691     
+ Misses        17174    16119    -1055     
+ Partials       4715     4634      -81     

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