Delete BBM backfill_project_id_for_projects_with_pipeline_variables backport to 17.11

Related: #537325 (closed)

What does this MR do and why?

This is a backport to %17.11

Delete BBM backfill_project_id_for_projects_with_pipeline_variables

BackfillProjectIdForProjectsWithPipelineVariables: p_ci_pipeline_variables background migration stuck at 0.00%

As discussed in: &16522 (comment 2492640881) and &16522 (comment 2486485883)

Batched migration to set pipeline_variables_minimum_override_role to no_one_allowed - Most like will be canceled as discussed with @fabiopitino. Because Restrict use of pipeline variables, will be left only for new namespaces.

Following up - #537325 (closed) the main regression issue it would be enough just to delete the BBM backfill_project_id_for_projects_with_pipeline_variables and backport to %17.11

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
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