remove ciflow_should_run (#70321)
Summary:
This PR implements the workflow changes described in https://fb.quip.com/oi8wAvajpR4g. Combined with the bot logic in https://github.com/suo/torchci/commit/d9285493367d3d62c9f731a800098c41fe6bdd75 (can be moved to probot but is easier to test there), it fully implements the proposal.
The CIFlow comment is slightly outdated now but is still technically correct (all the commands will continue to work as before, just through a different mechanism).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70321
Reviewed By: atalman, janeyx99
Differential Revision: D33690370
Pulled By: suo
fbshipit-source-id: 8d81ffeb249cdae53c5526798a4a504560d0204f
(cherry picked from commit 5ed8d0dfae6dcf8bacaf6e4229e7b40b5c2b2446)
