Fix not trigger FT on api-ref update

This patch fixes an issue that triggered the sol-kubernetes related job
when the file under ``api-ref`` folder is updated.

Signed-off-by: Ayumu Ueha <ueha.ayumu@fujitsu.com>
Change-Id: I1b360eff07bd2677dfc2003a7105187cd1d8a721

.zuul.yaml

@@ -528,11 +528,6 @@
       zuul_work_dir: src/opendev.org/openstack/tacker
       zuul_copy_output:
         '{{ devstack_log_dir }}/kubernetes': 'logs'
-    irrelevant-files:
-      - ^.*\.rst$
-      - ^doc/.*$
-      - ^releasenotes/.*$
-      - ^contrib/.*$
 
 - job:
     name: tacker-functional-devstack-multinode-sol-kubernetes-multi-tenant