Revert "Preprocess some unicode characters in MathJax (see #7)"

This reverts commit e45cbe5c74.

dollar.rkt

@@ -287,10 +287,8 @@ EOTEX
          (list (tex-addition tex-commands)
                'exact-chars)))
 
-;; TODO: handle delayed elements here instead of just flattening.
 (define ($-mathjax strs)
-  (elem #:style math-inline-style-mathjax
-        (map katex-convert-unicode (flatten strs))))
+  (elem #:style math-inline-style-mathjax strs))
 
 (define ($-katex strs)
   (elem #:style math-inline-style-katex