Remove unused sbom_components.source_package_name in post migration

What does this MR do and why?

This migration completes the process to remove the unused source_package_name column from the sbom_components table. Closes #435733.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

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Before

gitlabhq_development=# \d sbom_components
                                           Table "public.sbom_components"
       Column        |           Type           | Collation | Nullable |                   Default
---------------------+--------------------------+-----------+----------+---------------------------------------------
 id                  | bigint                   |           | not null | nextval('sbom_components_id_seq'::regclass)
 created_at          | timestamp with time zone |           | not null |
 updated_at          | timestamp with time zone |           | not null |
 component_type      | smallint                 |           | not null |
 name                | text                     |           | not null |
 purl_type           | smallint                 |           |          |
 source_package_name | text                     |           |          |
Indexes:
    "sbom_components_pkey" PRIMARY KEY, btree (id)
    "index_sbom_components_on_component_type_name_and_purl_type" UNIQUE, btree (name, purl_type, component_type)
Check constraints:
    "check_91a8f6ad53" CHECK (char_length(name) <= 255)
    "check_e2dcb53709" CHECK (char_length(source_package_name) <= 255)
Referenced by:
    TABLE "sbom_occurrences" CONSTRAINT "fk_d857c6edc1" FOREIGN KEY (component_id) REFERENCES sbom_components(id) ON DELETE CASCADE
    TABLE "sbom_component_versions" CONSTRAINT "fk_rails_61a83aa892" FOREIGN KEY (component_id) REFERENCES sbom_components(id) ON DELETE CASCADE

After

gitlabhq_development=# \d sbom_components
                                         Table "public.sbom_components"
     Column     |           Type           | Collation | Nullable |                   Default
----------------+--------------------------+-----------+----------+---------------------------------------------
 id             | bigint                   |           | not null | nextval('sbom_components_id_seq'::regclass)
 created_at     | timestamp with time zone |           | not null |
 updated_at     | timestamp with time zone |           | not null |
 component_type | smallint                 |           | not null |
 name           | text                     |           | not null |
 purl_type      | smallint                 |           |          |
Indexes:
    "sbom_components_pkey" PRIMARY KEY, btree (id)
    "index_sbom_components_on_component_type_name_and_purl_type" UNIQUE, btree (name, purl_type, component_type)
Check constraints:
    "check_91a8f6ad53" CHECK (char_length(name) <= 255)
Referenced by:
    TABLE "sbom_occurrences" CONSTRAINT "fk_d857c6edc1" FOREIGN KEY (component_id) REFERENCES sbom_components(id) ON DELETE CASCADE
    TABLE "sbom_component_versions" CONSTRAINT "fk_rails_61a83aa892" FOREIGN KEY (component_id) REFERENCES sbom_components(id) ON DELETE CASCADE

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Checkout branch and run bundle exec rails db:migrate
2. Open up psql and verify that the column is dropped from the table.
3. Revert migration, and verify that the column and column constraint recreates previous empty column: bundle exec rails db:rollback:main.