Process structures refactoring in runtime and libunit.

Generic process-to-process shared memory exchange is no more required.  Here,
it is transformed into a router-to-application pattern.  The outgoing shared
memory segments collection is now the property of the application structure.
The applications connect to the router only, and the process only needs to group
the ports.

src/nxt_process.c

@@ -146,7 +146,6 @@ nxt_process_child_fixup(nxt_task_t *task, nxt_process_t *process)
         }
 
         nxt_port_mmaps_destroy(&p->incoming, 0);
-        nxt_port_mmaps_destroy(&p->outgoing, 0);
 
     } nxt_runtime_process_loop;