CLEANUP: thread: rename __decl_hathreads() to __decl_thread()

I can never figure whether it takes an "s" or not, and in the end it's
better if it matches the file's naming, so let's call it "__decl_thread".
diff --git a/include/types/dns.h b/include/types/dns.h
index 0a8bf72..f504f5f 100644
--- a/include/types/dns.h
+++ b/include/types/dns.h
@@ -197,7 +197,7 @@
 	struct eb_root query_ids;           /* tree to quickly lookup/retrieve query ids currently in use
                                              * used by each nameserver, but stored in resolvers since there must
                                              * be a unique relation between an eb_root and an eb_node (resolution) */
-	__decl_hathreads(HA_SPINLOCK_T lock);
+	__decl_thread(HA_SPINLOCK_T lock);
 	struct list list;                   /* resolvers list */
 };