Use `inhibit-read-only' in Tramp

* lisp/net/tramp.el (tramp-process-actions, tramp-accept-process-output)
(tramp-send-string):
* lisp/net/tramp-adb.el (tramp-adb-handle-make-process)
(tramp-adb-send-command-and-check, tramp-adb-wait-for-output):
* lisp/net/tramp-sh.el (tramp-sh-handle-make-process)
(tramp-wait-for-output, tramp-send-command-and-check):
* lisp/net/tramp-smb.el (tramp-smb-wait-for-output):
Use `inhibit-read-only'.

lisp/net/tramp-adb.el

@@ -1091,7 +1091,7 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
 		    ;; otherwise we might be interrupted by
 		    ;; `verify-visited-file-modtime'.
 		    (let ((buffer-undo-list t)
-			  (buffer-read-only nil)
+			  (inhibit-read-only t)
 			  (mark (point)))
 		      (clear-visited-file-modtime)
 		      (narrow-to-region (point-max) (point-max))
@@ -1242,7 +1242,7 @@ the exit status is not equal 0, and t otherwise."
     (skip-chars-forward "^ ")
     (prog1
 	(zerop (read (current-buffer)))
-      (let (buffer-read-only)
+      (let ((inhibit-read-only t))
 	(delete-region (match-beginning 0) (point-max))))))
 
 (defun tramp-adb-barf-unless-okay (vec command fmt &rest args)
@@ -1260,7 +1260,7 @@ FMT and ARGS are passed to `error'."
     (if (tramp-wait-for-regexp
 	 proc timeout
 	 (tramp-get-connection-property proc "prompt" tramp-adb-prompt))
-	(let (buffer-read-only)
+	(let ((inhibit-read-only t))
 	  (goto-char (point-min))
 	  ;; ADB terminal sends "^H" sequences.
 	  (when (re-search-forward "<\b+" (point-at-eol) t)

lisp/net/tramp-sh.el

@@ -2906,7 +2906,7 @@ the result will be a local, non-Tramp, file name."
 		    ;; otherwise we might be interrupted by
 		    ;; `verify-visited-file-modtime'.
 		    (let ((buffer-undo-list t)
-			  (buffer-read-only nil)
+			  (inhibit-read-only t)
 			  (mark (point-max)))
 		      (clear-visited-file-modtime)
 		      (narrow-to-region (point-max) (point-max))
@@ -5081,7 +5081,7 @@ function waits for output unless NOOUTPUT is set."
 	   (regexp1 (format "\\(^\\|\000\\)%s" regexp))
 	   (found (tramp-wait-for-regexp proc timeout regexp1)))
       (if found
-	  (let (buffer-read-only)
+	  (let ((inhibit-read-only t))
 	    ;; A simple-minded busybox has sent " ^H" sequences.
 	    ;; Delete them.
 	    (goto-char (point-min))
@@ -5128,7 +5128,7 @@ DONT-SUPPRESS-ERR is non-nil, stderr won't be sent to /dev/null."
     (skip-chars-forward "^ ")
     (prog1
 	(zerop (read (current-buffer)))
-      (let (buffer-read-only)
+      (let ((inhibit-read-only t))
 	(delete-region (match-beginning 0) (point-max))))))
 
 (defun tramp-barf-unless-okay (vec command fmt &rest args)

lisp/net/tramp-smb.el

@@ -2029,7 +2029,7 @@ If ARGUMENT is non-nil, use it as argument for
 Removes smb prompt.  Returns nil if an error message has appeared."
   (with-current-buffer (tramp-get-connection-buffer vec)
     (let ((p (get-buffer-process (current-buffer)))
-	  buffer-read-only)
+	  (inhibit-read-only t))
 
       ;; Read pending output.
       (while (tramp-accept-process-output p 0.1))

lisp/net/tramp.el

@@ -4074,7 +4074,7 @@ connection buffer."
 	    (t "Login failed")))))
       (when (numberp pos)
 	(with-current-buffer (tramp-get-connection-buffer vec)
-	  (let (buffer-read-only) (delete-region pos (point))))))))
+	  (let ((inhibit-read-only t)) (delete-region pos (point))))))))
 
 ;;; Utility functions:
 
@@ -4083,7 +4083,8 @@ connection buffer."
 This is needed in order to hide `last-coding-system-used', which is set
 for process communication also."
   (with-current-buffer (process-buffer proc)
-    (let (buffer-read-only last-coding-system-used
+    (let ((inhibit-read-only t)
+	  last-coding-system-used
 	  ;; We do not want to run timers.
 	  timer-list timer-idle-list
 	  result)
@@ -4186,7 +4187,7 @@ the remote host use line-endings as defined in the variable
     (with-current-buffer (tramp-get-connection-buffer vec)
       ;; Clean up the buffer.  We cannot call `erase-buffer' because
       ;; narrowing might be in effect.
-      (let (buffer-read-only) (delete-region (point-min) (point-max)))
+      (let ((inhibit-read-only t)) (delete-region (point-min) (point-max)))
       ;; Replace "\n" by `tramp-rsh-end-of-line'.
       (setq string
 	    (mapconcat