nmcs-http: remove the timeout once expired

libcurl's documentation for CURLMOPT_TIMERFUNCTION requires the
application to install a non-repeating timer.

https://curl.haxx.se/libcurl/c/CURLMOPT_TIMERFUNCTION.html

So let's remove the GSource once expired.

Fixes: 69f048bf ('cloud-setup: add tool for automatic IP configuration in cloud')
(cherry picked from commit e09bd233)
(cherry picked from commit b7d53f0d)
(cherry picked from commit 92bded74)

clients/cloud-setup/nm-http-client.c

@@ -654,7 +654,7 @@ static gboolean
 _mhandle_timeout_cb (gpointer user_data)
 {
 	_mhandle_action (user_data, CURL_SOCKET_TIMEOUT, 0);
-	return G_SOURCE_CONTINUE;
+	return G_SOURCE_REMOVE;
 }
 
 static int