Remove calls to `to_loc_exn` in `saved_state.ml`
Remove calls to `to_loc_exn` in `saved_state.ml`

Summary: These were innocuous, but it's still better practice to avoid them.

Reviewed By: gabelevi

Differential Revision: D16770114

fbshipit-source-id: ac3baf24c5af3d11a848280c0d14c19bdfd47fc2

samwgoldman/flow,mroch/flow,gabelevi/flow,samwgoldman/flow,mroch/flow,facebook/flow,gabelevi/flow,facebook/flow,mroch/flow,mroch/flow,gabelevi/flow,gabelevi/flow,facebook/flow,samwgoldman/flow,mroch/flow,samwgoldman/flow,mroch/flow,gabelevi/flow,samwgoldman/flow,mroch/flow,gabelevi/flow,facebook/flow,gabelevi/flow,facebook/flow,facebook/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow