Remove ignore_column "id_convert_to_bigint"

What does this MR do and why?

Related to #442307 (closed)

id_convert_to_bigint was removed from the system_note_metadata table in !145125 (merged). This MR cleans up the ignore_column directive.

gitlabhq_development=# \d system_note_metadata
                                              Table "public.system_note_metadata"
         Column         |            Type             | Collation | Nullable |                     Default                      
------------------------+-----------------------------+-----------+----------+--------------------------------------------------
 commit_count           | integer                     |           |          | 
 action                 | character varying           |           |          | 
 created_at             | timestamp without time zone |           | not null | 
 updated_at             | timestamp without time zone |           | not null | 
 description_version_id | bigint                      |           |          | 
 note_id                | bigint                      |           | not null | 
 id                     | bigint                      |           | not null | nextval('system_note_metadata_id_seq'::regclass)
Indexes:
    "system_note_metadata_pkey" PRIMARY KEY, btree (id)
    "index_system_note_metadata_on_description_version_id" UNIQUE, btree (description_version_id) WHERE description_version_id IS NOT NULL
    "index_system_note_metadata_on_note_id" UNIQUE, btree (note_id)
Foreign-key constraints:
    "fk_d83a918cb1" FOREIGN KEY (note_id) REFERENCES notes(id) ON DELETE CASCADE
    "fk_fbd87415c9" FOREIGN KEY (description_version_id) REFERENCES description_versions(id) ON DELETE SET NULL
Referenced by:
    TABLE "resource_link_events" CONSTRAINT "fk_2a039c40f4" FOREIGN KEY (system_note_metadata_id) REFERENCES system_note_metadata(id) ON DELETE CASCADE