Bug Report: Noisy `vtexplain` log output about vitess

[dbussink]

With #15275 & #15279 the tests don't throw a large amount of error logs anymore and they are also 10x faster to run.

This change causes a significant slowdown in vtexplain: #14364

I think this is a red herring or at least some side effect of the bug in #15275 that somehow GRPC connections were made. Since vtexplain is all memory, no network connections are made so I'm not sure how this is related to the problem.

I think we should try again with the above fixes to see if there's still a problem or not.

[tycol7]

This change causes a significant slowdown in vtexplain: #14364

This change introduces the repeated vtexplain_vttablet.go:778] vtexplain: invalid column .column_name, tableColumnMap +map[:map[]] log lines: #13312

[tycol7]

Tested on sample data and running fast again. Thank you!