Remove FF `ci_support_reset_skipped_jobs_for_multiple_jobs`

What does this MR do and why?

This MR removes the feature flag ci_support_reset_skipped_jobs_for_multiple_jobs which was successfully globally rolled out in #410415 (closed).

This feature updates ResetSkippedJobsService so that it can support multiple jobs as input.

How to set up and validate locally

All processes that call ResetSkippedJobsService should behave as expected. There should be no visible change in pipeline processing.

We can test with a simple pipeline example to ensure it works:

1. Update your .gitlab-ci.yml file with the following contents: test.yml
2. Run the pipeline and notice the skipped jobs.

3. Play the manual job and observe that all the skipped jobs transition to "created" status.

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.

Related to #410415 (closed)