chore: remove RunKit

This service is dead.

> Sometime in November 2023, I observed that new packages and package versions uploaded to NPM stopped being updated on RunKit. > I don’t believe this project is being actively maintained anymore, though it would be delightful if that changed.

https://discuss.runkit.com/t/cant-run-on-runkit-unavaible/4976

If we decide to re-introduce something like runkit, let's make it in a way that will
continue to work, despite aquisitions and so on.

See https://howtomarketagame.com/2021/11/01/dont-build-your-castle-in-other-peoples-kingdoms/

Let's remove it for now, so at least the JS console won't have errors.

Author: mroderick

docs/_includes/embed-scripts.html

@@ -1,6 +1,4 @@
 <script src="{{ "/assets/js/prism.js" | prepend: site.baseurl }}"></script>
-<script src="https://embed.runkit.com"></script>
-{% include embed-scripts.html %}
 
 <div class="footer">
   <div class="container text-center">

docs/_includes/footer.html

@@ -1,12 +1,12 @@
 {
   "name": "examples",
   "version": "1.0.0",
-  "description": "Simulate running the Sinon runnable examples in RunKit",
+  "description": "Simulate running the Sinon runnable examples",
   "scripts": {
     "test": "./run-test.sh"
   },
   "license": "ISC",
-  "// dependencies": "We use 'latest' for the versions, as that is what RunKit will use",
+  "// dependencies": "We use 'latest' for the versions",
   "dependencies": {
     "@fatso83/mini-mocha": "latest",
     "@sinonjs/referee": "latest",