Remove self-hosted runners in ci_workflow_gen

[frouioui]

Description

We have not used any self-hosted runners for years, and now we benefit from larger runners thanks to CNCF which is what the self-hosted runners were trying to fix.

@GuptaManan100 let me know if that sounds correct to you.

[vitess-bot]

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[GuptaManan100]

I think its okay to remove them if we aren't using them.