simplify devcontainer config

.devcontainer/Dockerfile

@@ -1,4 +0,0 @@
-# NOTE: see https://hub.docker.com/_/microsoft-vscode-devcontainers
-ARG VARIANT="buster"
-FROM mcr.microsoft.com/vscode/devcontainers/rust:1-${VARIANT}
-RUN sudo apt update && sudo apt install -y cmake

.devcontainer/devcontainer.json

@@ -1,9 +1,7 @@
 {
 	"name": "Rust",
-  "build": {
+	"image": "mcr.microsoft.com/devcontainers/rust:1-buster",
-    "dockerfile": "Dockerfile",
+	"extensions": [
-    "args": { "VARIANT": "buster" }
+		"EditorConfig.EditorConfig"
-  },
+	]
-  "extensions": ["EditorConfig.EditorConfig"],
-  "remoteUser": "vscode"
 }