Remove unneeded creation of support_bot in specs

What does this MR do and why?

This is the first MR to change the way we fetch the support_bot from a global support_bot to an organization one.

This change removes unnecessary test setup code from multiple test files across the GitLab codebase. The removed code was creating a "support bot" user during test initialization to avoid database query counting issues and transaction conflicts. However, this setup appears to no longer be needed, so it's being cleaned up from 15 different test files including those testing work item operations, issue management, markdown rendering, and API functionality. This is a maintenance change that simplifies the test code without affecting the actual application behavior.

References

This is related to #565281. As we need to fetch the support_bot by organization, firstly I will clean all the unneeded setup and then follow with more MRs to change the way we fetch the support_bot

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How to set up and validate locally

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