Resolve "Address the Primary Key Overflow risk for the ci_build_trace_chunks 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_cf2f9e35f002 from the ci_build_trace_chunks table.

migration up:

== 20210906100316 DropTemporaryColumnsAndTriggersForCiBuildTraceChunks: migrating
-- remove_column("ci_build_trace_chunks", "build_id_convert_to_bigint")
   -> 0.0012s
== 20210906100316 DropTemporaryColumnsAndTriggersForCiBuildTraceChunks: migrated (0.0220s)

migration down:

== 20210906100316 DropTemporaryColumnsAndTriggersForCiBuildTraceChunks: reverting
-- table_exists?("ci_build_trace_chunks")
   -> 0.0005s
-- column_exists?("ci_build_trace_chunks", :id)
   -> 0.0014s
-- column_exists?("ci_build_trace_chunks", "build_id")
   -> 0.0008s
-- columns("ci_build_trace_chunks")
   -> 0.0011s
-- add_column("ci_build_trace_chunks", "build_id_convert_to_bigint", :int, {:default=>0, :null=>false})
   -> 0.0023s
== 20210906100316 DropTemporaryColumnsAndTriggersForCiBuildTraceChunks: reverted (0.0418s)

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Does this MR meet the acceptance criteria?

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• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
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• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
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• This change is backwards compatible across updates, or this does not apply.

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Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #338069 (closed)