Don't store execution result to a unused content-buf var

Fixes a warning:

    In go-play-region:
    go-mode.el:2137:13: Warning: Unused lexical variable ‘content-buf’

Author: Hi-Angel

go-mode.el

@@ -2133,19 +2133,18 @@ code to the Playground. You can disable the confirmation by setting
             (encode-coding-string
              (buffer-substring-no-properties start end)
              'utf-8))
-
-           (content-buf (url-retrieve
-                         "https://play.golang.org/share"
-                         (lambda (arg)
-                           (cond
-                            ((equal :error (car arg))
-                             (signal 'go-play-error (cdr arg)))
-                            (t
-                             (re-search-forward "\n\n")
-                             (let ((url (format "https://play.golang.org/p/%s"
-                                                (buffer-substring (point) (point-max)))))
-                               (when go-play-browse-function
-                                 (funcall go-play-browse-function url))))))))))))
+           (url-retrieve
+            "https://play.golang.org/share"
+            (lambda (arg)
+              (cond
+               ((equal :error (car arg))
+                (signal 'go-play-error (cdr arg)))
+               (t
+                (re-search-forward "\n\n")
+                (let ((url (format "https://play.golang.org/p/%s"
+                                   (buffer-substring (point) (point-max)))))
+                  (when go-play-browse-function
+                    (funcall go-play-browse-function url)))))))))))
 
 ;;;###autoload
 (defun go-download-play (url)