Remove case-flipping config

I never actually use it (I mostly wrote it to impress Ava) so time for
it to be relegated to the git history.

config.org

@@ -1487,98 +1487,6 @@
      (setq god-exempt-predicates nil)
    #+end_src
 
-** Case-flipping
-   Want to be able to toggle the 'shiftedness' of a selected region,
-   that is, map uppercase to lowercase and vice versa, but also map
-   things like '1' to '!' and '[' to '{'.
-
-   I doubt there's anything in Emacs already that has that mapping for
-   non-alphabetic characters, so first thing to do is define that:
-
-   #+begin_src emacs-lisp
-     (defvar non-letter-case-mapping
-       '((?1 . ?!) (?2 . ?\") (?3 . ?£) (?4 . ?$) (?5 . ?%)
-         (?6 . ?^) (?7 . ?&) (?8 . ?*) (?9 . ?\() (?0 . ?\))
-         (?- . ?_) (?= . ?+) (?\` . ?¬) (?\\ . ?\|) (?\[ . ?{)
-         (?\] . ?}) (?\; . ?:) (?\' . ?@) (?\# . ?~) (?\, . ?<)
-         (?\. . ?>) (?/ . ??)))
-   #+end_src
-
-   And then, a function to toggle a non-letter character, using that
-   mapping, defaulting to the identity if there's no entry.
-
-   #+begin_src emacs-lisp
-     (defun flip-non-letter-case (c)
-         (let (value)
-           (dolist (case-pair non-letter-case-mapping value)
-             (cond ((eq (car case-pair) c)
-                    (setq value (cdr case-pair)))
-                   ((eq (cdr case-pair) c)
-                    (setq value (car case-pair)))))
-           (when (eq value nil)
-             (setq value c))
-           value))
-   #+end_src
-
-   A similar function for letters can be easily defined using [[help:upcase][upcase]]
-   and [[help:downcase][downcase]]:
-
-   #+begin_src emacs-lisp
-     (defun upper-case-p (c)
-       (eq (upcase c) c))
-
-     (defun flip-letter-case (c)
-       (if (upper-case-p c)
-           (downcase c)
-         (upcase c)))
-   #+end_src
-
-   These can then be combined into a case-flipping function that will
-   work for both letters and non-letters:
-
-   #+begin_src emacs-lisp
-     (defun letter-p (c)
-       (and (characterp c)
-            (let ((uc (upcase c)))
-              (and (>= uc ?A) (<= uc ?Z)))))
-
-     (defun flip-char-case (c)
-       (if (letter-p c)
-           (flip-letter-case c)
-         (flip-non-letter-case c)))
-   #+end_src
-
-   ~flip-char-case~ can then applied over a whole string:
-
-   #+begin_src emacs-lisp
-     (defun flip-string-case (s)
-       (let ((len (length s))
-             (i 0))
-         (while (< i len)
-           (aset s i (flip-char-case (aref s i)))
-           (setq i (1+ i)))
-         s))
-   #+end_src
-
-   Finally, this can then be applied to the region, if it's active:
-
-   #+begin_src emacs-lisp
-     (defun flip-region-case ()
-       (interactive)
-       (when (region-active-p)
-         (let* ((start (region-beginning))
-                (end (region-end))
-                (text (buffer-substring-no-properties start end)))
-           (delete-region start end)
-           (insert (flip-string-case text)))))
-   #+end_src
-
-   And of course, I need a keybinding for that:
-
-   #+begin_src emacs-lisp
-     (global-set-key (kbd "C-~") 'flip-region-case)
-   #+end_src
-
 * Fin
   Now that start-up is finished, [[help:gc-cons-threshold][gc-cons-threshold]] and
   [[help:gc-cons-percentage][gc-cons-percentage]] need to be set back to reasonable values to avoid