Revert devcontainer bug workaround (#4206)

.devcontainer/dotnet/devcontainer.json

@@ -1,10 +1,6 @@
 {
   "name": "C# (.NET)",
-  //"image": "mcr.microsoft.com/devcontainers/dotnet",
-  // Workaround for https://github.com/devcontainers/images/issues/1752
-  "build": {
-    "dockerfile": "dotnet.Dockerfile"
-  },
+  "image": "mcr.microsoft.com/devcontainers/dotnet",
   "features": {
     "ghcr.io/devcontainers/features/azure-cli:1.2.9": {},
     "ghcr.io/devcontainers/features/github-cli:1": {

.devcontainer/dotnet/dotnet.Dockerfile

@@ -1,5 +0,0 @@
-FROM mcr.microsoft.com/devcontainers/universal:latest
-
-# Remove Yarn repository with expired GPG key to prevent apt-get update failures
-# Tracking issue: https://github.com/devcontainers/images/issues/1752
-RUN rm -f /etc/apt/sources.list.d/yarn.list