Remove CentOS 8 from CI. (#4134)

Author: felixfontein

.azure-pipelines/azure-pipelines.yml

@@ -221,8 +221,6 @@ stages:
               test: centos6
             - name: CentOS 7
               test: centos7
-            - name: CentOS 8
-              test: centos8
             - name: Fedora 32
               test: fedora32
             - name: Fedora 33
@@ -249,8 +247,6 @@ stages:
         parameters:
           testFormat: 2.10/linux/{0}
           targets:
-            - name: CentOS 8
-              test: centos8
             - name: Fedora 32
               test: fedora32
             - name: openSUSE 15 py3
@@ -270,8 +266,6 @@ stages:
         parameters:
           testFormat: 2.9/linux/{0}
           targets:
-            - name: CentOS 8
-              test: centos8
             - name: Fedora 31
               test: fedora31
             - name: openSUSE 15 py3