Remove duplicated outdated copies of slint.tmLanguage.json

There should be only one copy of our textmate grammar.
Our grammar evolve and we shouldn't keep copies around which will be
forgotten to be updated.

docs/astro/ec.config.mjs

@@ -188,7 +188,10 @@ export default {
     shiki: {
         langs: [
             JSON.parse(
-                fs.readFileSync("src/misc/Slint-tmLanguage.json", "utf-8"),
+                fs.readFileSync(
+                    "../../editors/vscode/slint.tmLanguage.json",
+                    "utf-8",
+                ),
             ),
         ],
     },