Update find_opt to use Map.find_opt
Update find_opt to use Map.find_opt

Summary: Removed a TODO like a good boy scout :D

Reviewed By: mroch

Differential Revision: D9967600

fbshipit-source-id: 13c7b0245b72efdcaaa89d4ba41216612668a589

popham/flow,facebook/flow,mroch/flow,samwgoldman/flow,AgentME/flow,gabelevi/flow,jamesgpearce/flow,samwgoldman/flow,gabelevi/flow,samwgoldman/flow,gabelevi/flow,gabelevi/flow,AgentME/flow,samwgoldman/flow,mroch/flow,popham/flow,jamesgpearce/flow,jamesgpearce/flow,mroch/flow,facebook/flow,mroch/flow,mroch/flow,samwgoldman/flow,facebook/flow,popham/flow,facebook/flow,facebook/flow,popham/flow,gabelevi/flow,popham/flow,popham/flow,gabelevi/flow,AgentME/flow,jamesgpearce/flow,mroch/flow,gabelevi/flow,jamesgpearce/flow,facebook/flow,popham/flow,samwgoldman/flow,AgentME/flow,jamesgpearce/flow,AgentME/flow,jamesgpearce/flow,mroch/flow,facebook/flow,samwgoldman/flow