Refactor out map.el usage

After some profiling, it turns out map-put and map-delete are 5-7x
slower (more on Emacs 25) than delq, setf/alist-get and add-to-list for
small lists (under 250 items), which is exactly how I've been using
them.

The only caveat is alist-get's signature is different on Emacs 25, thus
a polyfill is necessary in core-lib.

modules/lang/org/+babel.el

@@ -36,7 +36,7 @@ string). Stops at the first function to return non-nil.")
                                         (or (cdr (assq lang +org-babel-mode-alist))
                                             lang)))
                         nil t)))
-          (map-put org-babel-load-languages lang t))
+          (add-to-list 'org-babel-load-languages (cons lang t)))
         t)))
   (advice-add #'org-babel-confirm-evaluate :around #'+org*babel-lazy-load-library)