Revert "Use the PD leader member in server if it's not in etcd members (#7753)"

[JmPotato]

What problem does this PR solve?

Issue Number: ref #7752.

What is changed and how does it work?

This reverts commit d3b93074bc0b33c9899e3322b82b77538c57ed67 from #7753.

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• CabinfeverB

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[JmPotato]

/merge

[ti-chi-bot]

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/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 055f45f

[codecov]

Codecov Report

Merging #7755 (055f45f) into master (d3b9307) will decrease coverage by 0.15%.
The diff coverage is 85.71%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7755      +/-   ##
==========================================
- Coverage   70.26%   70.11%   -0.15%     
==========================================
  Files         430      430              
  Lines       47645    47641       -4     
==========================================
- Hits        33476    33402      -74     
- Misses      11410    11501      +91     
+ Partials     2759     2738      -21     

Flag	Coverage Δ
unittests	70.11% <85.71%> (-0.15%)	⬇️

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