API: libstonithd: Deprecate stonith_api_operations_t

...and struct stonith_api_operations_s, and all of its members.

There are no known external users. Any externally relevant functionality
should either already exist in libpacemaker or be added there. The
libstonithd fencing API should be for internal use by other low-level
libraries.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>