remove Lwt from Types_js.parse_contents
remove Lwt from Types_js.parse_contents

Summary:
I wanted to use `parse_contents` separately from `type_contents`/`typecheck_contents` (e.g. to respond to LSP requests that don't need types) but didn't want its profiling stuff. pulling that out also let it not depend on Lwt, which will simplify other callers.

note: this doesn't even really belong in Types_js, except that it depends on Inference_utils and Flow_error which are part of the inference service. planning to clean this up further later.

Reviewed By: nmote

Differential Revision: D24220049

fbshipit-source-id: bb1b012ccfbc263deaba14ff84ede42b4cd0d21f

facebook/flow,facebook/flow,mroch/flow,mroch/flow,mroch/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,facebook/flow,mroch/flow,facebook/flow,mroch/flow