[MINOR] config: make it possible to specify a cookie even without a server

Since version 1.0.0, it's forbidden to have a cookie specified without at
least one server. This test is useless and makes it complex to write APIs
to iteratively generate working configurations. Remove the test.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index dedd5c7..9063854 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -5584,11 +5584,6 @@
 
 		case PR_MODE_HTTP:
 			curproxy->acl_requires |= ACL_USE_L7_ANY;
-			if ((curproxy->cookie_name != NULL) && (curproxy->srv == NULL)) {
-				Alert("config : HTTP proxy %s has a cookie but no server list !\n",
-				      curproxy->id);
-				cfgerr++;
-			}
 			break;
 		}