Remove github_import_project redis_hll tracking

What does this MR do and why?

This is the second part for the corresponding issue: Instrument all the end states of imports with G... (#381500)

The existing metrics were removed:

• 'redis_hll_counters.importer.github_import_project_start_monthly',
• 'redis_hll_counters.importer.github_import_project_success_monthly',
• 'redis_hll_counters.importer.github_import_project_failure_monthly'
• 'redis_hll_counters.importer.github_import_project_start_weekly',
• 'redis_hll_counters.importer.github_import_project_success_weekly',
• 'redis_hll_counters.importer.github_import_project_failure_weekly'

These metrics were implemented in the scope of !70012 (merged)

❗ It was replaced with snowplow events in the scope of !112062 (merged)

How to set up and validate locally

In the rails console check metrics Gitlab::Usage::ServicePingReport.for(output: :all_metrics_values), there should not be any metrics for importer like:

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.