Remove auto-fill-parameters experiment

See context here: https://codercom.slack.com/archives/CJURPL8DN/p1742905676562979?thread_ts=1742902799.767199&cid=CJURPL8DN

Additional motivation to remove this experiment is because its currently only enabled for the classic workspace creation flow and not dynamic parameters. This could cause confusion if anyone attempts to use the experiment.
