Get rid of an unnecessary `List.concat`
Get rid of an unnecessary `List.concat`

Summary: As requested in D7538928

Reviewed By: panagosg7

Differential Revision: D7607601

fbshipit-source-id: 6f85d3126fb6db1ba528e0a396358f1701337ff5

nmote/flow,claudiopro/flow,facebook/flow,mroch/flow,jamesgpearce/flow,gabelevi/flow,jamesgpearce/flow,samwgoldman/flow,JonathanUsername/flow,samwgoldman/flow,facebook/flow,facebook/flow,samwgoldman/flow,JonathanUsername/flow,gabelevi/flow,mroch/flow,jamesgpearce/flow,nmote/flow,popham/flow,gabelevi/flow,samwgoldman/flow,mroch/flow,jamesgpearce/flow,nmote/flow,facebook/flow,facebook/flow,mroch/flow,mroch/flow,jamesgpearce/flow,AgentME/flow,gabelevi/flow,claudiopro/flow,claudiopro/flow,nmote/flow,popham/flow,popham/flow,AgentME/flow,mroch/flow,JonathanUsername/flow,jamesgpearce/flow,samwgoldman/flow,nmote/flow,samwgoldman/flow,JonathanUsername/flow,popham/flow,AgentME/flow,JonathanUsername/flow,JonathanUsername/flow,samwgoldman/flow,gabelevi/flow,AgentME/flow,nmote/flow,mroch/flow,gabelevi/flow,popham/flow,claudiopro/flow,facebook/flow,nmote/flow,JonathanUsername/flow,jamesgpearce/flow,claudiopro/flow,gabelevi/flow,AgentME/flow,popham/flow,facebook/flow,popham/flow