fix(customs): stabilize flaky check_reputation integration test

[nshirley]

Because

• test/remote/check_reputation_tests.js intermittently failed in the nightly
  Integration Test. The flaky subtest (query reputation stub directly using ip-reputation-js-client) asserted timingPhases.total > 0, but the client
  computes that total from integer-millisecond Date.now() deltas, so a
  sub-millisecond localhost round-trip produced a 0ms total and failed the
  assertion.
• fxa-customs-server is no longer in active use, so the subtest isn't worth
  stabilizing.

This pull request

• Removes the flaky direct-client subtest and its now-unused repJSClient
  setup from check_reputation_tests.js. No source or other tests are touched.

Issue that this pull request solves

Closes: FXA-13959

Checklist

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• My commit is GPG signed.
• If applicable, I have modified or added tests which pass locally.
• I have added necessary documentation (if appropriate).
• I have verified that my changes render correctly in RTL (if appropriate).
• I have manually reviewed all AI generated code.

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Other information (Optional)

• Scoped deliberately small: only the flaky subtest is removed. The
  ipReputationClient.js source and the rest of the customs-server remain
  untouched for a future cleanup, since the service is no longer in active use.