Remove the deprecated ubuntu_18

Signed-off-by: Chin Yeung Li <[email protected]>

Author: chinyeungli

azure-pipelines.yml

@@ -5,17 +5,6 @@
 ################################################################################
 
 jobs:
-    - template: etc/ci/azure-posix.yml
-      parameters:
-          job_name: ubuntu18_cpython
-          image_name: ubuntu-18.04
-          python_versions: ['3.7', '3.8', '3.9', '3.10', '3.11']
-          test_suites:
-              all: |
-                  sudo apt-get -y update
-                  sudo apt-get -y install build-essential strace graphviz
-                  venv/bin/pytest -n 2 -vvs
-
     - template: etc/ci/azure-posix.yml
       parameters:
           job_name: ubuntu20_cpython