Removing appveyor.yml in favor of defaults

Removing this appveyor configuration in order to use the AppVeyor defaults which will use a Visual Studio 2017 only VM which is needed for chromium 66 and higher.

appveyor.yml

@@ -1,50 +0,0 @@
-version: 1.0.{build}
-build_cloud: libcc-20
-image: libcc-20-vs2017
-clone_folder: c:\build
-environment:
-  matrix:
-  - TARGET_ARCH: ia32
-    COMPONENT: shared_library
-  - TARGET_ARCH: x64
-    COMPONENT: shared_library
-  - TARGET_ARCH: ia32
-    COMPONENT: static_library
-  - TARGET_ARCH: x64
-    COMPONENT: static_library
-build_script:
-- ps: >-
-    if(($env:APPVEYOR_PULL_REQUEST_HEAD_REPO_NAME -split "/")[0] -eq ($env:APPVEYOR_REPO_NAME -split "/")[0]) {
-      Write-warning "Skipping PR build for branch"; Exit-AppveyorBuild
-    } else {
-      if($env:APPVEYOR_SCHEDULED_BUILD -eq 'True')  {
-        script\cibuild.ps1 -buildTests
-      } else {
-        script\cibuild.ps1
-      }
-      if ($? -ne 'True') {
-        throw "Build failed with exit code $?"
-      } else {
-        "Build succeeded."
-      }
-    }
-test_script:
-- ps: >-
-    if($env:COMPONENT -eq 'static_library' -And $env:APPVEYOR_SCHEDULED_BUILD -eq 'True')  {
-      python script\run_tests --generate_report -t $env:TARGET_ARCH
-      npm install -g junit-merge
-      junit-merge -d test_reports
-      # upload results to AppVeyor
-      $wc = New-Object 'System.Net.WebClient'
-      $wc.UploadFile("https://windows-ci.electronjs.org/api/testresults/junit/$($env:APPVEYOR_JOB_ID)", (Resolve-Path .\merged-test-results.xml))
-    } else {
-      Write-Output "Skipping tests for shared_library build"
-    }
-
-artifacts:
-- path: libchromiumcontent.zip
-  name: libchromiumcontent.zip
-- path: libchromiumcontent-static.zip
-  name: libchromiumcontent-static.zip
-- path: 'merged-test-results.xml'
-  name: tests