[CI] Remove centos-7 testing since it is EOL (#113896) (#113905)

(cherry picked from commit c475895)

Author: brianseeders

.buildkite/pipelines/periodic-packaging.template.yml

@@ -7,7 +7,6 @@ steps:
         matrix:
           setup:
             image:
-              - centos-7
               - debian-11
               - opensuse-leap-15
               - oraclelinux-7

.buildkite/pipelines/periodic-packaging.yml

@@ -8,7 +8,6 @@ steps:
         matrix:
           setup:
             image:
-              - centos-7
               - debian-11
               - opensuse-leap-15
               - oraclelinux-7

.buildkite/pipelines/periodic-platform-support.yml

@@ -7,7 +7,6 @@ steps:
         matrix:
           setup:
             image:
-              - centos-7
               - debian-11
               - opensuse-leap-15
               - oraclelinux-7

.buildkite/pipelines/pull-request/packaging-tests-unix.yml

@@ -10,7 +10,6 @@ steps:
         matrix:
           setup:
             image:
-              - centos-7
               - debian-11
               - opensuse-leap-15
               - oraclelinux-7
@@ -38,7 +37,6 @@ steps:
         matrix:
           setup:
             image:
-              - centos-7
               - debian-11
               - opensuse-leap-15
               - oraclelinux-7
@@ -66,7 +64,6 @@ steps:
         matrix:
           setup:
             image:
-              - centos-7
               - debian-11
               - opensuse-leap-15
               - oraclelinux-7