* lisp/org/ob-julia.el: Use lexical-binding

* lisp/org/ob-julia.el: Use lexical-binding

(ess-eval-visibly-p): Declare.
(org-babel-julia-assign-elisp): Remove unused vars `header` and
`row-names` and corespondingly remove now unused args `colnames-p` and
`rownames-p`.
(org-babel-variable-assignments:julia): Adjust call to
`org-babel-julia-assign-elisp` accordingly.
(org-babel-julia-initiate-session): Use `bound-and-true-p`.
(org-babel-julia-evaluate-external-process)
(org-babel-julia-evaluate-session, org-babel-julia-evaluate):
Remove unused arg `row-names-p`.
(org-babel-execute:julia): Adjust call to
`org-babel-julia-evaluate` accordingly.