Dvc: run: hide --file and --single-stage

[jorgeorpinel]

Report

Per https://github.com/iterative/dvc.org/pull/1420#discussion_r442644095:

--file is still in the help output of dvc run -h, mentions DVC-file (a concept we are removing), and makes no sense without --single-stage (which is hidden). Please hide both for now.

Please provide information about your setup

DVC 1.0

[efiop]

@jorgeorpinel --single-stage is already hidden. --file will likely be used in the future, but could hide it for now. Will send an update.

[jorgeorpinel]

Thanks!