Remove support for ubuntu-18.04 (#22795)

Author: wyunchi-ms

docker/Dockerfile-ubuntu-18.04

@@ -28,18 +28,10 @@ try {
     foreach ($dockerfile in (Get-ChildItem -Path $DOCKER -Filter "Dockerfile-*").FullName) {
         $os = $dockerfile.split("Dockerfile-")[1]
         Write-Output $os
-        if ($os -eq "ubuntu-18.04") {
-            docker build --build-arg VERSION=$version `
-                     --build-arg BUILD_DATE=$date `
-                     --tag $DockerImageName':'$version"-"$os `
-                     --tag $DockerImageName':latest' `
-                     -f $dockerfile $DOCKER
-        }else {
-            docker build --build-arg VERSION=$version `
-                     --build-arg BUILD_DATE=$date `
-                     --tag $DockerImageName':'$version"-"$os `
-                     -f $dockerfile $DOCKER
-        }
+        docker build --build-arg VERSION=$version `
+                    --build-arg BUILD_DATE=$date `
+                    --tag $DockerImageName':'$version"-"$os `
+                    -f $dockerfile $DOCKER
 
     }
 } catch {

tools/Docker/BuildImages.ps1

@@ -75,7 +75,6 @@ function Install-PowerShell {
 }
 
 # Image "macOS-10.15" preinstalled Az modules
-# Image "vs2017-win2016" and "ubuntu-18.04" preinstalled AzureRM modules. 
 
 # Remove Az.* modules
 . "$PSScriptRoot/Common.ps1"