[playground] fix jsoo_refmt_main, remove load_modules as not necessary

[jchavarri]

Adds "/static" to directory in jsoo_refmt_main (like jsoo_main).

Removes load_modules as it's not needed anymore. Using js_of_ocaml.bc build-fs creates a JS file that will add a file to jsoo pseudo file system directly when loaded, removing the need for providing an API hook on the compiler.

cc @ryyppy