Remove the <source> that messes it up in dark mode (devcontainers#90)

Fixes devcontainers#88

Nothing else changes when dark mode is enabled, so this is the only thing that does.
When it does, it makes it white-on-white which isn't readable.

The reason I removed the <picture> wrapper tag is just personal preference to not
use stuff if it's not needed; and it doesn't seem to be needed when you only have
one <img> and no <source> elements to provide alternatives 🤷‍♂️.

Author: jcbhmr

_includes/footer.html

@@ -28,10 +28,7 @@
                     <li>
                         <div class="copyright">
                             <a id="footer-microsoft-link" class="logo" href="https://www.microsoft.com">
-                                <picture>
-                                    <source srcset="{{site.baseurl}}/img/microsoft-logo.png" media="(prefers-color-scheme: dark)"></source>
-                                    <img src="{{site.baseurl}}/img/microsoft-logo-inverted.png" height="20" alt="Microsoft">
-                                </picture>
+                                <img src="{{site.baseurl}}/img/microsoft-logo-inverted.png" height="20" alt="Microsoft">
                             </a>
                             <span>© 2022 Microsoft</span>
                         </div>