Remove support for azure-pipelines (#2948)

At this point Actions PR CI and Push CI cover all tests in Azure Pipelines so they
are not needed.

.azure-pipelines.yml

@@ -1,104 +0,0 @@
-# C/C++ with GCC
-# Build your C/C++ project with GCC using make.
-# Add steps that publish test results, save build artifacts, deploy, and more:
-# https://docs.microsoft.com/vsts/pipelines/apps/c-cpp/gcc
-
-jobs:
-- job: Linux
-  pool:
-    vmImage: ubuntu-16.04
-    
-  steps:
-  - checkout: self
-    fetchDepth: 1
-    
-  - script:
-      make CPUS="2" PKGS="racket-test db-test unstable-flonum-lib net-test" CONFIGURE_ARGS_qq="$RACKET_CONFIGURE_ARGS"
-    displayName: 'make'
-    
-  - script: |
-      export PATH=$PATH:`pwd`/racket/bin
-      raco test -l tests/racket/test
-      racket -l tests/racket/contract/all
-      raco test -l tests/json/json
-      raco test -l tests/file/main
-      raco test -l tests/net/head
-      raco test -l tests/net/uri-codec
-      raco test -l tests/net/url
-      raco test -l tests/net/url-port
-      raco test -l tests/net/encoders
-      raco test -l tests/openssl/basic
-      raco test -l tests/openssl/https
-      raco test -l tests/match/main
-      raco test -l tests/zo-path
-      raco test -l tests/xml/test
-      raco test -l tests/db/all-tests
-      raco test -c tests/stxparse
-    displayName: test
-
-- job: Windows
-  pool:
-    vmImage: vs2015-win2012r2
-  
-  steps:
-  - checkout: self
-    fetchDepth: 1
-  
-  - script: |
-      call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\vc\vcvarsall.bat" x86
-      echo %cd%
-      nmake win32-in-place PKGS="racket-test unstable-flonum-lib net-test"
-    displayName: Build
-
-  - script: |
-      echo %cd%
-      racket\raco.exe pkg show -l
-      racket\racket.exe -l tests/racket/test
-      racket\racket.exe -l tests/racket/contract/all
-      racket\raco.exe test -l tests/json/json
-      racket\raco.exe test -l tests/file/main
-      racket\raco.exe test -l tests/net/head
-      racket\raco.exe test -l tests/net/uri-codec
-      racket\raco.exe test -l tests/net/url
-      racket\raco.exe test -l tests/net/url-port
-      racket\raco.exe test -l tests/net/encoders
-      racket\raco.exe test -l tests/openssl/basic
-      racket\raco.exe test -l tests/openssl/https
-      racket\raco.exe test -l tests/match/main
-      racket\raco.exe test -l tests/zo-path
-      racket\raco.exe test -l tests/xml/test
-      racket\raco.exe test -c tests/db/all-tests
-      racket\raco.exe test -c tests/stxparse
-    displayName: Test
-    
-- job: Mac
-  pool:
-    vmImage: 'macOS 10.13'
-  
-  steps:
-  - checkout: self
-    fetchDepth: 1
-  
-  - script:
-      make CPUS="2" PKGS="racket-test db-test unstable-flonum-lib net-test" CONFIGURE_ARGS_qq="$RACKET_CONFIGURE_ARGS"
-    displayName: 'make'
-    
-  - script: |
-      export PATH=$PATH:`pwd`/racket/bin
-      raco test -l tests/racket/test
-      racket -l tests/racket/contract/all
-      raco test -l tests/json/json
-      raco test -l tests/file/main
-      raco test -l tests/net/head
-      raco test -l tests/net/uri-codec
-      raco test -l tests/net/url
-      raco test -l tests/net/url-port
-      raco test -l tests/net/encoders
-      raco test -l tests/openssl/basic
-      raco test -l tests/openssl/https
-      raco test -l tests/match/main
-      raco test -l tests/zo-path
-      raco test -l tests/xml/test
-      raco test -l tests/db/all-tests
-      raco test -c tests/stxparse
-    displayName: test