zuul: remove "files" for openstack-tox-tht

openstack-tox-tht is a dependency of functional testing jobs, which can
be problematic now because it only runs if some files are touched.

If e.g. common/container_puppet.py is the only file that is changed,
zuul will complain because the dependency graph is broken.

Let's relax openstack-tox-tht to run all the times; and stay a
dependency of other functional testing jobs (which brings value).

Change-Id: I3f05ca26064a2897a724876033a5cc4a602c38a2

zuul.d/layout.yaml

@@ -148,6 +148,3 @@
       tox_envlist: tht
       bindep_profile: test tht
       test_setup_skip: true
-    files:
-      - ^((docker|puppet)/services|deployment)/.*$
-      - tools/*