counsel.el (counsel--call): Remove stderr guards

delete-file does not signal an error when given a non-existent file,
and guarding insert-file-contents is at best unnecessary and at
worst a race condition.

Re: abo-abo#1828

counsel.el

@@ -1339,13 +1339,12 @@ COMMAND fails.  Obey file handlers based on `default-directory'."
                (lwarn 'ivy :warning "%s"
                       (apply #'concat
                              (error-message-string res)
-                             (when (file-readable-p stderr)
-                               (insert-file-contents stderr nil nil nil t)
+                             (unless (zerop (cadr (insert-file-contents
+                                                   stderr nil nil nil t)))
                                (list "\n" (buffer-string)))))
                (signal (car res) (cdr res)))
              (buffer-substring (point-min) (- (point) (if (bolp) 1 0)))))
-      (when (file-exists-p stderr)
-        (delete-file stderr)))))
+      (delete-file stderr))))
 
 (defun counsel--git-grep-count-func-default ()
   "Default function to calculate `counsel--git-grep-count'."