gnus: move org-mime to org layer

org-mime is installed by org-plus-contrib so it makes more sense to
configure in org layer.

layers/+email/gnus/packages.el

@@ -83,17 +83,4 @@
       (kbd "J") 'gnus-summary-next-article
       (kbd "K") 'gnus-summary-prev-article
       (kbd "<RET>") 'spacemacs/browse-nnrss-url)))
-
-  ;; org-mime is initialized here because otherwise spacemacs
-  ;; complains that the org-mime package does not exist
-  (use-package org-mime
-    :defer t
-    :commands (org-mime-htmlize
-               org-mime-org-buffer-htmlize)
-    :init
-    (progn
-      ;; setup org-mime
-      (evil-leader/set-key-for-mode 'message-mode
-        "mh" 'org-mime-htmlize)
-      (evil-leader/set-key-for-mode 'org-mode
-        "mH" 'org-mime-org-buffer-htmlize))))
+  )

layers/org/packages.el

@@ -22,6 +22,8 @@
     (org :location built-in)
     org-plus-contrib
     org-bullets
+    ;; org-mime is installed by `org-plus-contrib'
+    (org-mime :location built-in)
     org-pomodoro
     org-present
     org-repo-todo
@@ -214,6 +216,17 @@ Will work on both org-mode and any mode that accepts plain html."
     :defer t
     :init (add-hook 'org-mode-hook 'org-bullets-mode)))
 
+(defun org/init-org-mime ()
+  (use-package org-mime
+    :defer t
+    :commands (org-mime-htmlize org-mime-org-buffer-htmlize)
+    :init
+    (progn
+      (evil-leader/set-key-for-mode 'message-mode
+        "mh" 'org-mime-htmlize)
+      (evil-leader/set-key-for-mode 'org-mode
+        "mH" 'org-mime-org-buffer-htmlize))))
+
 (defun org/init-org-pomodoro ()
   (use-package org-pomodoro
     :defer t