Remove unused ci_build_report_results_build_id_seq

Ref: #362984 (closed)

What does this MR do and why?

This MR removes an unused sequence generated by mistake when introducing our ci_build_report_results_builds table.

Why are we doing this?

We generated those sequences by mistake when setting the primary key by using a different column id.

We missed to set default: nil when creating associated migration as suggested by our documentation.

Setting default: nil will ensure a primary key sequence is not created, and since the primary key will automatically get an index, we set index: false to avoid creating a duplicate.

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