Remove the "you have not specified reviewers" prompt from the `arc` client
Remove the "you have not specified reviewers" prompt from the `arc` client

Summary:
Ref T4631. Ref T10939. I don't have any good solutions here; this is perhaps the least-bad one.

  - This prompt is misleading/confusing in the presence of Herald/Owners.
  - This prompt is likely of very little value for experienced reviewers.
  - When it works, this prompt may be of some value for new reviewers, but getting it wrong is probably more confusing than getting it right is helpful, and there is a more accurate version of the warning in the web UI that new users are likely to see.
  - In the long run, this code should not live in the client.

Test Plan: Created this revision without specifying reviewers, probably didn't get prompted.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4631, T10939

Differential Revision: https://secure.phabricator.com/D16139

chundongwang/arcanist,codelabs-ch/arcanist,aik099/arcanist,chundongwang/arcanist,fivestars/arcanist,fivestars/arcanist,fivestars/arcanist,haskell-infra/arcanist,Khan/arcanist,folsom-labs/arcanist,folsom-labs/arcanist,chundongwang/arcanist,uber/arcanist,chundongwang/arcanist,phacility/arcanist,r4nt/arcanist,phacility/arcanist,r4nt/arcanist,aik099/arcanist,Khan/arcanist,codelabs-ch/arcanist,aik099/arcanist,uber/arcanist,phacility/arcanist,r4nt/arcanist,Khan/arcanist,codelabs-ch/arcanist,haskell-infra/arcanist,phacility/arcanist,codelabs-ch/arcanist,haskell-infra/arcanist,uber/arcanist,r4nt/arcanist,aik099/arcanist,haskell-infra/arcanist,folsom-labs/arcanist,uber/arcanist,codelabs-ch/arcanist,phacility/arcanist,Khan/arcanist,fivestars/arcanist,folsom-labs/arcanist