Remove redundant config arg when launching pd

[ari-e]

What problem does this PR solve?

Redundant passing of --config command line argument to pd when launching playground.

What is changed and how it works?

Remove redundant line.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Ran manual test and it still works

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[CLAassistant]

All committers have signed the CLA.

[ti-chi-bot]

Welcome @ari-e! It looks like this is your first PR to pingcap/tiup 🎉

[kaaaaaaang]

/LGTM

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-27 08:17:27.858106283 +0000 UTC m=+2678001.615241856: ☑️ agreed by kaaaaaaang.