Remove SSL_TASK, the DECnet Based SSL Engine

This engine is for VMS only, and isn't really part of the core OpenSSL
but rather a side project of its own that just happens to have tagged
along for a long time.  The reasons why it has remained within the
OpenSSL source are long lost in history, and there not being any real
reason for it to remain here, it's time for it to move out.

This side project will appear as a project in its own right, the
location of which will be announced later on.

Reviewed-by: Tim Hudson <tjh@openssl.org>