[CI] Use lighter Emacs image, remove validation links in HTML

The docker image used is now Emacs on Alpine, which should be lighter
than the previous one.

The validation link is also now disabled in HTML exports.

.drone.yml

@@ -3,7 +3,7 @@ name: default
 
 steps:
 - name: build
-  image: silex/emacs:27
+  image: silex/emacs:27-alpine
   commands:
     - pwd
     - ls -ahl

export.el

@@ -6,7 +6,8 @@
 (package-install 'htmlize)
 (package-install 's)
 (require 's)
-(setq org-confirm-babel-evaluate nil)
+(setq org-confirm-babel-evaluate nil
+      org-html-validation-link nil)
 (let* ((files (mapcar #'expand-file-name
                       (file-expand-wildcards "org/config/*.org"))))
   (mapc (lambda (file)