Move lexical-binding setting into a hook

*scratch* still doesn't apply the (setq-default lexical-binding t) form, but
the advice I'd been giving `setup' broke the documentation generator function.
So I just added lexical-binding to a hook when opening an emacs-lisp-mode
buffer.

Will this bite me later?  Possibly.  But I'll deal with that then.  The worst
that could happen is that I'd write another function, `setup-test' or
something, that'd apply lexical-binding and then run `setup'.  Or I could just
set lexical-binding to t manually.  Whatever.

init.el

@@ -16,17 +16,6 @@
 
 ;;; Code:
 
-;; Let's use lexical binding by default, shall we?
-(setq-default lexical-binding t)
-
-;; For some reason, the above setting doesn't translate to the *scratch*
-;; buffer, where I try out packages.
-(advice-add 'setup :around
-            (defun acdw/setup-lexical-advice (orig-fun &rest args)
-              "Wrap `setup' in a `lexical-binding' form."
-              (let ((lexical-binding t))
-                (apply orig-fun args))))
-
 
 ;;; Necessary packages
 
@@ -843,6 +832,11 @@ if ripgrep is installed, otherwise `consult-grep'."
            eval-expression-print-level nil
            lisp-indent-function #'lisp-indent-function)
 
+  (defun acdw/enforce-lexical-binding ()
+    (setq lexical-binding t))
+
+  (add-hook 'emacs-lisp-mode-hook #'acdw/enforce-lexical-binding)
+
   (defun acdw/eval-region-or-buffer ()
     (interactive)
     (if (region-active-p)