Remove trace column from ci_builds table

What does this MR do and why?

Related to #18605 (closed)

The column was ignored in %15.4 by !96865 (merged)

This column is be safe to remove because it's not being used for writes since before %9.0 and in %11.0 it was added a background migration to archive existing builds with traces in the database.

On .com it looks like there are only two records that still have data stored this way: #18605 (comment 1058496381)

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Related to #18605 (closed)