bugfix: after scaling down a Raft cluster, the metadata still contains the removed node

[funky-eyes]

…m the metadata

• I have registered the PR changes.

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

fixes #6853

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov]

Codecov Report

Attention: Patch coverage is 11.53846% with 23 lines in your changes missing coverage. Please review.

Project coverage is 52.30%. Comparing base (963f7f3) to head (2cf3d4d).
Report is 1 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...he/seata/server/cluster/raft/RaftStateMachine.java	11.53%	22 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x    #6855      +/-   ##
============================================
- Coverage     52.31%   52.30%   -0.01%     
- Complexity     6412     6414       +2     
============================================
  Files          1083     1083              
  Lines         37918    37923       +5     
  Branches       4494     4492       -2     
============================================
+ Hits          19836    19837       +1     
- Misses        16113    16114       +1     
- Partials       1969     1972       +3     

Files with missing lines	Coverage Δ
...in/java/org/apache/seata/common/metadata/Node.java	62.50% <ø> (ø)
...he/seata/server/cluster/raft/RaftStateMachine.java	14.73% <11.53%> (+0.12%)	⬆️

... and 3 files with indirect coverage changes

[xingfudeshi]

LGTM