Fix custom.el writing to DOOMDIR/init.el too early

This would cause ~/.doom.d/init.el to exist before `doom quickstart` can
copy ~/.emacs.d/init.example.el into it, causing some newcomers to
experience a wrong-type-argument: hash-table-p error at startup (and no
modules being enabled).

core/autoload/packages.el

@@ -621,8 +621,3 @@ calls."
 
 ;;;###autoload
 (advice-add #'package-install-selected-packages :override #'doom//install)
-
-;; Don't save `package-selected-packages' to `custom-file'
-;;;###autoload
-(advice-add #'package--save-selected-packages :override
-            (lambda (&optional value) (if value (setq package-selected-packages value))))

core/core-packages.el

@@ -62,6 +62,10 @@ missing) and shouldn't be deleted.")
         ("melpa-mirror" . -2)
         ("gnu" . -3)))
 
+;; Don't save `package-selected-packages' to `custom-file'
+(advice-add #'package--save-selected-packages :override
+            (lambda (&optional value) (if value (setq package-selected-packages value))))
+
 (when (or (not gnutls-verify-error)
           (not (ignore-errors (gnutls-available-p))))
   (dolist (archive package-archives)