Remove --providers from --help output for Mbed TLS

Remove --providers from --help output for Mbed TLS

This option is OpenSSL-only. When used with Mbed TLS, it prints warnings
and does not do anything. With this change, the option is still parsed,
to ensure compatiblity of configurations, but it is removed from the
--help text.

Change-Id: I0f56ca69efae0ca376eb9eae064a893c8768188e
Signed-off-by: Max Fillinger <maximilian.fillinger@sentyron.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1799
Message-Id: <20260722163800.2474-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg37781.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>