mu4e-compose: simplify buffer creation

Seems we can avoid the advising of message-pop-to-buffer.

mu4e/mu4e-compose.el

@@ -745,19 +745,6 @@ Based on the value of `mu4e-compose-switch'."
     ;; t for backward compatibility with mu4e-compose-in-new-frame
     (_             (mu4e-error "Invalid mu4e-compose-switch"))))
 
-(defun mu4e--fake-pop-to-buffer (name &optional _switch)
-  "A fake `message-pop-to-buffer' for creating buffer NAME.
-This is a little glue to use `message-reply', `message-forward'
-etc. We cannot use the normal `message-pop-to-buffer' since we're
-not ready yet to show the buffer in mu4e."
-  ;; note: we're in a _different_ buffer here, so we need to copy
-  ;; message-reply-header's buffer-local value.
-  (let ((reply-headers message-reply-headers))
-    (set-buffer (get-buffer-create name))
-    (setq-local message-reply-headers reply-headers)
-    (erase-buffer)
-    (current-buffer)))
-
 (defun mu4e--headers (compose-type)
   "Determine headers needed for message based on COMPOSE-TYPE."
   (seq-filter #'identity ;; ensure needed headers are generated.
@@ -790,15 +777,9 @@ PARENT is the \"parent\" message; nil
                   gnus-message-replyencrypt nil
                   gnus-message-replysignencrypted nil)
       (goto-char (point-min))
-      ;; annoyingly, various message- functions call `message-pop-to-buffer`
-      ;; (showing the message. But we're not ready for that yet. So
-      ;; temporarily override that.
-      (advice-add 'message-pop-to-buffer
-                  :override #'mu4e--fake-pop-to-buffer)
       (funcall compose-func parent)
       ;; add some more headers, if needed.
       (message-generate-headers (mu4e--headers compose-type))
-      (advice-remove 'message-pop-to-buffer #'mu4e--fake-pop-to-buffer)
       (current-buffer)))) ;; returns new buffer (this is not the tmp buf)