ci: Remove macOS 10.14 pipelines on Azure Pipelines

See https://devblogs.microsoft.com/devops/hosted-pipelines-image-deprecation/

Author: ubolonton

.azure-pipelines/main.yml

@@ -21,17 +21,6 @@ strategy:
     # windows-2019:
     #   IMAGE_NAME: 'windows-2019'
 
-    # Sometimes fails: TLS issue against melpa.org and ftpmirror.gnu.org.
-    # macos-10.14-emacs-25.3:
-    #   IMAGE_NAME: 'macos-10.14'
-    #   EVM_EMACS: emacs-25.3
-    macos-10.14-emacs-26.3:
-      IMAGE_NAME: 'macos-10.14'
-      EVM_EMACS: emacs-26.3
-    macos-10.14-emacs-27.1:
-      IMAGE_NAME: 'macos-10.14'
-      EVM_EMACS: emacs-27.1
-
     # Always fails: ValueError: Could not determine the version of Emacs at emacs
     # macos-10.15-emacs-25.3:
     #   IMAGE_NAME: 'macos-10.15'