docs: Relates to Issue #995. Fix links in existing documentation (#999)

* docs: Remove safe-mix since is no longer local dependency

* docs: Fix existing packages link. Still only includes Substrate Core

substrate/core/consensus/rhd/src/lib.rs

@@ -14,6 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
 
+// tag::description[]
 //! BFT Agreement based on a rotating proposer in different rounds.
 //!
 //! Where this crate refers to input stream, should never logically conclude.
@@ -29,6 +30,7 @@
 //! conclude without having witnessed the conclusion.
 //! In general, this future should be pre-empted by the import of a justification
 //! set for this block height.
+// end::description[]
 
 #![cfg(feature = "rhd")]