SecureTransport is now the default SSL backend on OS X.
Users can still choose the OpenSSL backend by passing the -openssl,
-openssl-linked or -no-securetransport option to configure script.

[ChangeLog][Important Behavior Change] Make SecureTransport the default SSL backend on OS X

Change-Id: I7a4edfdb72e63975d6b31435969702f8e86a10f2
Reviewed-by: Richard J. Moore <rich@kde.org>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@theqtcompany.com>