CNDB-15969 Remove duplicate SystemDistributedKeyspace calls missed during rebase of STAR-993 on Apache Cassandra 5.0.4

[djatnieks]

What is the issue

Fixes CNDB-15969

What does this PR fix and why was it fixed

Removes duplicate SystemDistributedKeyspace calls in RepairSession that were missed during STAR-993 rebase.

[github-actions]

Checklist before you submit for review

• This PR adheres to the Definition of Done
• Make sure there is a PR in the CNDB project updating the Converged Cassandra version
• Use NoSpamLogger for log lines that may appear frequently in the logs
• Verify test results on Butler
• Test coverage for new/modified code is > 80%
• Proper code formatting
• Proper title for each commit staring with the project-issue number, like CNDB-1234
• Each commit has a meaningful description
• Each commit is not very long and contains related changes
• Renames, moves and reformatting are in distinct commits
• All new files should contain the DataStax copyright header instead of the Apache License one

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-2117 rejected by Butler

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2 regressions found
See build details here

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Found 2 new test failures

Test	Explanation	Runs	Upstream
paxos_test.TestPaxos.test_contention_many_threads (offheap-bti)	REGRESSION	🔴	0 / 16
replica_side_filtering_test.TestAllowFiltering.test_consistent_wide_table (offheap-bti)	REGRESSION	🔴	0 / 16

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Found 5 known test failures