Remove temporary hack for persistent connection
Remove temporary hack for persistent connection

Summary:
This hasn't been needed since Flow v0.43 so I think it's been long enough that
we can officially drop support. The persistent connection is still experimental
anyway so I don't think we need a lot of backwards compatibility.

Reviewed By: ljw1004

Differential Revision: D5165814

fbshipit-source-id: 1408f701234927c97167e8dbc4e7c2744540cbea

popham/flow,JonathanUsername/flow,facebook/flow,facebook/flow,popham/flow,TiddoLangerak/flow,MichaelDeBoey/flow,fletcherw/flow,JonathanUsername/flow,facebook/flow,ylu1317/flow,facebook/flow,nmote/flow,fletcherw/flow,fletcherw/flow,nmote/flow,JonathanUsername/flow,ylu1317/flow,nmote/flow,popham/flow,TiddoLangerak/flow,facebook/flow,jamesgpearce/flow,claudiopro/flow,MichaelDeBoey/flow,mroch/flow,facebook/flow,nmote/flow,mroch/flow,nmote/flow,mroch/flow,fletcherw/flow,JonathanUsername/flow,MichaelDeBoey/flow,gabelevi/flow,claudiopro/flow,ylu1317/flow,samwgoldman/flow,TiddoLangerak/flow,AgentME/flow,AgentME/flow,mroch/flow,samwgoldman/flow,popham/flow,TiddoLangerak/flow,facebook/flow,jamesgpearce/flow,JonathanUsername/flow,AgentME/flow,AgentME/flow,claudiopro/flow,jamesgpearce/flow,samwgoldman/flow,gabelevi/flow,samwgoldman/flow,nmote/flow,claudiopro/flow,TiddoLangerak/flow,jamesgpearce/flow,JonathanUsername/flow,mroch/flow,MichaelDeBoey/flow,mroch/flow,ylu1317/flow,mroch/flow,popham/flow,JonathanUsername/flow,samwgoldman/flow,fletcherw/flow,gabelevi/flow,MichaelDeBoey/flow,jamesgpearce/flow,jamesgpearce/flow,gabelevi/flow,popham/flow,gabelevi/flow,AgentME/flow,popham/flow,gabelevi/flow,nmote/flow,jamesgpearce/flow,fletcherw/flow,gabelevi/flow,samwgoldman/flow,samwgoldman/flow,ylu1317/flow,claudiopro/flow