etcdutil: revert etcd client in pd legacy server

[lhy1024]

What problem does this PR solve?

Issue Number: Close #6124

What is changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Related changes

• Need to cherry-pick to the release branch

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• bufferflies
• rleungx

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[codecov]

Codecov Report

Patch coverage: 91.30% and project coverage change: -0.07 ⚠️

Comparison is base (220dbed) 74.53% compared to head (469ba03) 74.47%.

❗ Current head 469ba03 differs from pull request most recent head afa43ed. Consider uploading reports for the commit afa43ed to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6182      +/-   ##
==========================================
- Coverage   74.53%   74.47%   -0.07%     
==========================================
  Files         394      394              
  Lines       38644    38660      +16     
==========================================
- Hits        28804    28791      -13     
- Misses       7293     7314      +21     
- Partials     2547     2555       +8     

Flag	Coverage Δ
unittests	74.47% <91.30%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/mcs/tso/server/server.go	50.16% <ø> (ø)
pkg/utils/etcdutil/etcdutil.go	79.73% <90.47%> (+0.90%)	⬆️
pkg/mcs/resource_manager/server/server.go	57.32% <100.00%> (ø)
server/server.go	73.85% <100.00%> (-1.09%)	⬇️

... and 23 files with indirect coverage changes

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[lhy1024]

/merge

[ti-chi-bot]

@lhy1024: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

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

Commit hash: 469ba03

[ti-chi-bot]

@lhy1024: Your PR was out of date, I have automatically updated it for you.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.0: #6186.