Make `C-a' in enriched-mode behave more line in other modes

* lisp/textmodes/enriched.el (enriched-mode-map): Don't rebind
beginning-or-line, because it makes `C-S-a' not mark the region,
and it doesn't allow actually moving to the beginning of the line
if the line starts with characters in `adaptive-fill-regexp'
(bug#22554).

lisp/textmodes/enriched.el

@@ -186,7 +186,6 @@ The value is a list of \(VAR VALUE VAR VALUE...).")
 
 (defvar enriched-mode-map
   (let ((map (make-sparse-keymap)))
-    (define-key map [remap move-beginning-of-line] 'beginning-of-line-text)
     (define-key map "\C-m" 'reindent-then-newline-and-indent)
     (define-key map
       [remap newline-and-indent] 'reindent-then-newline-and-indent)