CI: Remove centos-7 jobs

CentOS 7 will go EOL later this year, and infra wants to drop the nodes
soon-ish -- don't make them wait on our account.

Change-Id: Iaa31fc95ed2d100726adf60807c8bf95599afd3f

.zuul.yaml

@@ -13,14 +13,6 @@
       Build and run test and valgrind-test for liberasurecode
       on arm64.
 
-- job:
-    name: liberasurecode-unittests-centos-7
-    parent: liberasurecode-unittests
-    nodeset: centos-7
-    description: |
-      Build and run test and valgrind-test for liberasurecode.
-      This job runs on CentOS-7.
-
 - job:
     name: liberasurecode-unittests-centos-8-stream
     parent: liberasurecode-unittests
@@ -57,7 +49,6 @@
     check:
       jobs:
         - liberasurecode-unittests
-        - liberasurecode-unittests-centos-7
         - liberasurecode-unittests-centos-8-stream
         - liberasurecode-unittests-centos-9-stream
         - liberasurecode-unittests-centos-9-stream-fips
@@ -68,7 +59,6 @@
     gate:
       jobs:
         - liberasurecode-unittests
-        - liberasurecode-unittests-centos-7
         - liberasurecode-unittests-centos-8-stream
         - liberasurecode-unittests-centos-9-stream
         - liberasurecode-unittests-centos-9-stream-fips