removed tutorial

because I had to change the part where it said that the browser does not support the background size

Author: josemoracard

exercises/04.1-Combined-Rules/README.md

@@ -1,7 +1,3 @@
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-tutorial: "https://youtu.be/watch?v=uQS5QeEE-B4"
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 # `04.1` Combined Rules
 
 CSS files take up space on your server and also take time to download (like everything); it is yet another text document that the browser has to download before rendering the page, which is why it's important to keep the CSS document as small as possible.