textprox/expat2: update to 2.4.1 -- fixes CVE-2013-0340/CWE-776

See [1] for details:
Expat 2.4.0 and follow-up release 2.4.1 have both been released earlier
today (21-05-23). Release 2.4.0 fixes long known security issue CVE-2013-0340 by
adding protection against so-called Billion Laughs Attacks, a form of
denial of service against applications accepting XML input, in all known
variations, including recent flavor Parameter Laughs.

[1] https://blog.hartwork.org/posts/cve-2013-0340-billion-laughs-fixed-in-expat-2-4-0

PR: 256121
Exp-run by: antoine