Remove tripleo-centos-7 nodesets

We no longer have tripleo-test-cloud-rh1 online, these nodesets can be
removed.

Change-Id: Ie3879cf3f8bdc3c569226a6d89876fe06bc330d0
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

zuul.d/nodesets.yaml

@@ -29,12 +29,6 @@
       - name: opensuse-423
         label: opensuse-423
 
-- nodeset:
-    name: tripleo-centos-7
-    nodes:
-      - name: tripleo-centos-7
-        label: tripleo-centos-7
-
 - nodeset:
     name: ubuntu-bionic
     nodes:
@@ -149,12 +143,6 @@
       - name: primary
         label: opensuse-423
 
-- nodeset:
-    name: legacy-tripleo-centos-7
-    nodes:
-      - name: primary
-        label: tripleo-centos-7
-
 - nodeset:
     name: legacy-ubuntu-trusty
     nodes: