Make join_results branch into the join block even when only one edge is live.

I don't don't totally understand the implications of this but it makes the
behavior consistent for all live edges, which is going to make joining the
arms of an alt expression work correctly.

src/comp/middle/trans.rs

@@ -3045,12 +3045,6 @@ fn join_results(@block_ctxt parent_cx,
             ret ins.(0);
         }
 
-        case (1u) {
-            // Only one incoming edge is live, so we just feed that block
-            // onward.
-            ret live.(0);
-        }
-
         case (_) { /* fall through */ }
     }