Remove custom TLS 1.0 PRF implementation only used by LibreSSL/wolfSSL

Remove custom TLS 1.0 PRF implementation only used by LibreSSL/wolfSSL

After the removal of the OpenSSL 1.0.2 support, LibreSSL/wolfSSL are the
only libraries that still needs the custom implementation.

Since our LibreSSL/wolfSSL support is always best effort, we can afford to
limit LibreSSL support in this way. If they want to support this, they
should expose the functionality as well.

Change-Id: I5bfa3630ad4dff2807705658bc877c4a429a39ce
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20240515100115.11056-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg28672.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>