tasks/inference.py: remove flag from bilby_pipe_gracedb

This fixes https://sentry.io/organizations/ligo-caltech/issues/1308898441/?project=1425216&referrer=AssignedActivityEmail or https://gracedb-playground.ligo.org/apiweb/superevents/MS191101p/files/pe_dag.log,0.

@shanika.galaudage Could you please open a MR when the conda environment is updated?