[macOS] Remove macOS 10.14 related code in the VE repo (#4816)

* [MacOS] Remove code for macOS-10.14

* remove is_Less_BigSur in all script

* remove variable the IsLessThanBigSur

images.CI/macos/azure-pipelines/macos1014.yml

@@ -1,23 +0,0 @@
-name: macOS-10.14_$(date:yyyyMMdd)$(rev:.r)_unstable
-schedules:
-- cron: "0 0 * * *"
-  displayName: Daily
-  branches:
-    include:
-    - main
-  always: true
-
-trigger: none
-pr:
-  autoCancel: true
-  branches:
-    include:
-    - main
-
-jobs:
-- template: image-generation.yml
-  parameters:
-    image_label: 'macOS Mojave'
-    base_image_name: 'clean-macOS-10.14-380Gb_runner'
-    template_path: 'templates/macOS-10.14.json'
-    target_datastore: 'ds-image'