Improved support for js_of_ocaml + OCaml 4.03+

[SanderSpies]

I did this so Reason can build be with JSOO on OCaml 4.04.2.

• Remove dependency on utop as this should be optional
• Rename vendored easy_format.ml to easy_format_vendored.ml to avoid warning 31, which became the default from OCaml 4.03+ but can't be disabled with JSOO.
• Fix reason_without_utop.mllib which included duplicate stuff from reasonparser.mllib

[chenglou]

Cool. So what happens if folks install Reason and expect rtop? And what about reason-cli

The bspack thing is likely broken. I can fix it later.

[jordwalke]

Great! As far as optional dependency on utop, I believe that opam is deprecating that feature (optional dependencies).

The test is failing because it can't find utop. I think the right step is to completely factor out rtop into its own opam package (it wouldn't need to be updated frequently IIRC).

(reason-cli can still aggregate all the tools we want but there's no reason why the core Reason tool for syntax should include a command line.)

[bsansouci]

I want this PR because the profilers I'd like to use require 4.03. (https://github.com/LexiFi/landmarks)