Step 1/2 of OpenSSL remove: Suppress building

Step 1/2 of OpenSSL remove: Suppress building

As of now, the NO_OPENSSL directive has been replaced with an undocumented
FORCE_OPENSSL directive.  Unless FORCE_OPENSSL is defined in make.conf,
the OpenSSL libraries, headers, and man pages will no longer be built and
installed.

Existing OpenSSL files will remain installed unless REMOVE_OPENSSL_FILES
is defined for the upgrade command, e.g.
> make upgrade REMOVE_OPENSSL_FILES=yes

It is recommended that all remaining programs and libraries linked to the
base OpenSSL libraries be rebuilt to use one of the DPorts SSL libraries.
The DPorts packages have been built with DPorts LibreSSL for a few weeks
now, so ensuring all installed packages are reinstalled or rebuilt will be
sufficient for most users, but don't forget about software built outside
of DPorts.

The OpenSSL sources and makefiles will be removed within a month (step 2),
but FORCE_OPENSSL will work in the meantime to continue building OpenSSL
although it will receive no further updates.