magit-cmd-output: do not corrupt output

This fixes #544.  There is no reason why we would want to manipulate
git's output.  In the master and next branches something similar to
the code removed in this commit was used to have colorful graphs in
logs, but in maint that isn't the case.

magit.el

@@ -879,13 +879,12 @@ Read `completing-read' documentation for the meaning of the argument"
   (insert (magit-cmd-output cmd args)))
 
 (defun magit-cmd-output (cmd args)
-  (let ((cmd-output (with-output-to-string
-                      (with-current-buffer standard-output
-                        (apply #'process-file
-                               cmd
-                               nil (list t nil) nil
-                               args)))))
-    (replace-regexp-in-string "\e\\[.*?m" "" cmd-output)))
+  (with-output-to-string
+    (with-current-buffer standard-output
+      (apply #'process-file
+             cmd
+             nil (list t nil) nil
+             args))))
 
 (defun magit-git-string (&rest args)
   (magit-trim-line (magit-git-output args)))