Remove Gratipay icon (#847)

The project stopped in 2017, see:
https://gratipay.news/the-end-cbfba8f50981

_data/simple-icons.json

@@ -670,11 +670,6 @@
             "hex": "E10098",
             "source": "http://graphql.org/"
         },
-        {
-            "title": "Gratipay",
-            "hex": "663300",
-            "source": "https://gratipay.com"
-        },
         {
             "title": "Grav",
             "hex": "221E1F",

icons/gratipay.svg

@@ -1 +0,0 @@
-<svg aria-labelledby="simpleicons-gratipay-icon" role="img" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><title id="simpleicons-gratipay-icon">Gratipay icon</title><path d="M24 12c0 6.629-5.37 12-12 12-6.627 0-12-5.373-12-12S5.373 0 12 0c6.63 0 12 5.369 12 12zm-7.119-4.523c-1.35-.891-2.634-.216-3.306.566-.252.291-.681.635-1.492.635-.811 0-1.241-.346-1.491-.635-.66-.781-1.95-1.455-3.301-.566-1.574 1.047-1.125 2.936-.659 3.48l5.46 7.393 5.46-7.393c.464-.545.93-2.434-.661-3.48h-.01z"/></svg>