mu4e: use builtin function "shr-render-region" for simplicity

mu4e/mu4e-message.el

@@ -268,7 +268,7 @@ point in eiter the headers buffer or the view buffer."
   "Html to text using the shr engine; this can be used in
 `mu4e-html2text-command' in a new enough emacs. Based on code by
 Titus von der Malsburg."
-  (interactive)
+  (interactive)
   (let (
 	 ;; When HTML emails contain references to remote images,
 	 ;; retrieving these images leaks information. For example,
@@ -277,8 +277,7 @@ Titus von der Malsburg."
 	 ;; to not retrieve images.
 	 ;; See this discussion on mu-discuss:
 	 ;; https://groups.google.com/forum/#!topic/mu-discuss/gr1cwNNZnXo
-	 (shr-inhibit-images t))
-    (erase-buffer)
+	 (shr-inhibit-images t))
     (shr-render-region (point-min) (point-max))
     (goto-char (point-min))))