### What changes were proposed in this pull request?
This patch removes TODO comments which are left to address changing case classes having vars to normal classes in spark-sql-kafka module - the pattern is actually discouraged, but still worth to break it, as we already use automatic toString implementation and we may be using more.
### Why are the changes needed?
Described above.
### Does this PR introduce any user-facing change?
No.
### How was this patch tested?
Existing UTs.
Closes#26992 from HeartSaVioR/SPARK-30337.
Authored-by: Jungtaek Lim (HeartSaVioR) <kabhwan.opensource@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
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