[examples] Use more semantic footer element (#35033)

Use more semantic footer element for example blog footer. Also remove unused styles. No visual changes.



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [x] Make sure the linting passes by running `yarn lint`


Co-authored-by: JJ Kasper <22380829+ijjk@users.noreply.github.com>

examples/blog/theme.config.js

@@ -2,20 +2,19 @@ const YEAR = new Date().getFullYear()
 
 export default {
   footer: (
-    <small style={{ display: 'block', marginTop: '8rem' }}>
-      <time>{YEAR}</time> © Your Name.
-      <a href="/feed.xml">RSS</a>
+    <footer>
+      <small>
+        <time>{YEAR}</time> © Your Name.
+        <a href="/feed.xml">RSS</a>
+      </small>
       <style jsx>{`
+        footer {
+          margin-top: 8rem;
+        }
         a {
           float: right;
         }
-        @media screen and (max-width: 480px) {
-          article {
-            padding-top: 2rem;
-            padding-bottom: 4rem;
-          }
-        }
       `}</style>
-    </small>
+    </footer>
   )
 }