chore: align expected node engine with volta (#7998)

**Related Issue:** n/a

## Summary
Trying to build the Calcite Design System packages with node 16 fails.
Removing the node>engine from <root>/package.json and updating the docs to direct contributors to reference Volta for their node development enviornment.

CONTRIBUTING.md

@@ -97,7 +97,7 @@ Our code base is written in TypeScript and must adhere to specific conventions a
 
 ## Getting a development environment set up
 
-An installation of Node is required for development. If you don't have Node installed, we recommend [Volta](https://docs.volta.sh/guide/getting-started), which will automatically use the Node/NPM versions pinned at the bottom of [`package.json`](./package.json). If you prefer a different Node version manager, make sure to use the major versions of Node/NPM specified in [`package.json`](./package.json).
+An installation of Node is required for development. If you don't have Node installed, we recommend [Volta](https://docs.volta.sh/guide/getting-started), which will automatically use the Node/NPM versions pinned at the bottom of [`package.json`](./package.json). If you prefer a different Node version manager, make sure to use the major versions of Node/NPM specified under the "volta" key in [`package.json`](./package.json).
 
 We also recommend installing the following extensions in your editor of choice: TypeScript, TailwindCSS, ESLint, Stylelint, and Prettier. If you use VS Code, you will see a pop up in the bottom right corner prompting you to install or view the workspaces's recommended extensions. Here are instructions for manually installing the extensions in a variety of editors:
 

package.json

@@ -111,9 +111,6 @@
     "workbox-build": "7.0.0"
   },
   "license": "SEE LICENSE.md",
-  "engines": {
-    "node": ">=16.0.0"
-  },
   "packageManager": "[email protected]",
   "volta": {
     "node": "18.18.0",