BUG/MINOR: proxy: fix email-alert leak on deinit()

proxy email-alert settings weren't cleaned up in free_proxy(), resulting
in small memory leak if "email-alert to" or "email-alert from" were used
on a regular or default proxy.

It may be backported to all stable versions.

src/proxy.c

@@ -220,6 +220,7 @@ void free_proxy(struct proxy *p)
 	istfree(&p->monitor_uri);
 	istfree(&p->server_id_hdr_name);
 	free(p->rdp_cookie_name);
+	free_email_alert(p);
 	free(p->invalid_rep);
 	free(p->invalid_req);
 #if defined(CONFIG_HAP_TRANSPARENT)