id128: change table header from "uuid" to just "id"

The tool deals with any kind of 128bit id, not just uuid, and by default
we display just a series of hex chars, hence let's not claim everything
was a "uuid", but just generically say "id"

src/id128/id128.c

@@ -87,7 +87,7 @@ static int show_one(Table **table, const char *name, sd_id128_t uuid, bool first
 
         } else {
                 if (!*table) {
-                        *table = table_new("name", "uuid");
+                        *table = table_new("name", "id");
                         if (!*table)
                                 return log_oom();
                         table_set_width(*table, 0);