Resolve "Address the Primary Key Overflow risk for the ci_build_needs table - Step 3: Drop temporary columns and triggers"

What does this MR do?

This MR removes the column build_id_convert_to_bigint and the trigger trigger_21e7a2602957 from the ci_build_needs table.

migration up:

== 20210902144144 DropTemporaryColumnsAndTriggersForCiBuildNeeds: migrating ===
-- remove_column("ci_build_needs", "build_id_convert_to_bigint")
   -> 0.0010s
== 20210902144144 DropTemporaryColumnsAndTriggersForCiBuildNeeds: migrated (0.0222s)

migration down:

== 20210902144144 DropTemporaryColumnsAndTriggersForCiBuildNeeds: reverting ===
-- add_column("ci_build_needs", "build_id_convert_to_bigint", :int, {:default=>0, :null=>false})
   -> 0.0038s
== 20210902144144 DropTemporaryColumnsAndTriggersForCiBuildNeeds: reverted (0.0488s)

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Does this MR meet the acceptance criteria?

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Related to #338060 (closed)