list: make our list macros a bit easier to use by not requring type spec on each invocation

We can determine the list entry type via the typeof() gcc construct, and
so we should to make the macros much shorter to use.

src/systemctl/systemctl.c

@@ -3019,7 +3019,7 @@ static int status_property(const char *name, DBusMessageIter *iter, UnitStatusIn
                                         return r;
                                 }
 
-                                LIST_PREPEND(ExecStatusInfo, exec, i->exec, info);
+                                LIST_PREPEND(exec, i->exec, info);
 
                                 dbus_message_iter_next(&sub);
                         }
@@ -3474,7 +3474,7 @@ static int show_one(const char *verb,
         }
 
         while ((p = info.exec)) {
-                LIST_REMOVE(ExecStatusInfo, exec, info.exec, p);
+                LIST_REMOVE(exec, info.exec, p);
                 exec_status_info_free(p);
         }