Use `cirrusci/windowsservercore:2016` container for CI (#18202)

* Use `cirrusci/windowsservercore:2016` container for CI

with 4 CPUs

* Removed `Dockerfile.windows`

.cirrus.yml

@@ -39,7 +39,9 @@ task:
   env:
     SHARD: tests
   windows_container:
-    dockerfile: dev/bots/docker/Dockerfile.windows
+    image: cirrusci/windowsservercore:2016
+    os_version: 2016
+    cpu: 4
   env:
     CIRRUS_WORKING_DIR: "C:\\Windows\\Temp\\flutter sdk"
   git_fetch_script: git fetch origin

dev/bots/docker/Dockerfile.windows

-FROM microsoft/windowsservercore:1709
-
-SHELL ["powershell", "-Command", "$ErrorActionPreference = 'Stop'; $ProgressPreference = 'SilentlyContinue';"]
-
-RUN netsh interface ipv4 set subinterface 'vEthernet (Ethernet)' mtu=1460 store=persistent
-
-RUN Set-ExecutionPolicy Bypass -Scope Process -Force; iex ((New-Object System.Net.WebClient).DownloadString('https://chocolatey.org/install.ps1'))
-
-RUN choco install -y git
-
-SHELL ["cmd", "/S", "/C"]
-
-RUN setx /m PATH "%PATH%;C:\nodejs"
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