MINOR: Fix ShareGroupCommandTest reset-offsets tests passing invalid --from-file scope combination

[joshua2519]

Two tests from #22197 combined --from-file with
--topic/--all-topics,which ShareGroupCommandOptions.checkArgs
forbids — allResetOffsetsScopeOpts makes {--topic, --all-topics, --from-file} mutually exclusive, enforced via checkInvalidArgs. The
tests only passed because a leaked no-op Exit procedure swallowed the
resulting printUsageAndExit. - Drop --topic/--all-topics from
both tests' import args so --from-file is the sole scope. - Adjust
describeTopics count 6 → 5 in testResetOffsetsExportImportPlan (no
--topic means partitions come from listShareGroupOffsets).

Test-only; no production changes.

Reviewers: Andrew Schofield aschofield@confluent.io

[AndrewJSchofield]

Thanks for the PR. lgtm