remove Alpine test validation

Author: ctaggart

azure-pipelines.yml

@@ -17,10 +17,6 @@ resources:
     image: andrewarnott/linux-buildagent
   - container: bionic
     image: microsoft/dotnet:2.1-sdk-bionic
-  - container: alpine38
-    image: mcr.microsoft.com/dotnet/core/sdk:2.1.505-alpine3.8
-  - container: alpine39
-    image: mcr.microsoft.com/dotnet/core/sdk:2.1.505-alpine3.9
 
 jobs:
 - job: Windows
@@ -142,26 +138,6 @@ jobs:
   steps:
   - template: azure-pipelines/xplattest-pipeline.yml
 
-- job: Alpine_3_8
-  dependsOn: Windows
-  pool:
-    vmImage: Ubuntu 16.04 # not a bug. we always use this pool, but use containers for the specific version
-  container: alpine38
-  steps:
-  - script: apk update && apk add git
-    displayName: Installing git
-  - template: azure-pipelines/xplattest-pipeline.yml
-
-- job: Alpine_3_9
-  dependsOn: Windows
-  pool:
-    vmImage: Ubuntu 16.04 # not a bug. we always use this pool, but use containers for the specific version
-  container: alpine39
-  steps:
-  - script: apk update && apk add git
-    displayName: Installing git
-  - template: azure-pipelines/xplattest-pipeline.yml
-
 - job: macOS
   dependsOn: Windows
   pool: