docs: Don't recommend TypeScript type assertions for reactive declarations (#8824)

strictly speaking that's not the same and could hide some type errors

Author: Not-Jayden

documentation/docs/05-misc/03-typescript.md

@@ -176,16 +176,14 @@ You cannot type your reactive declarations with TypeScript in the way you type a
 </script>
 ```
 
-You cannot add a `: TYPE` because it's invalid syntax in this position. Instead, you can use the `as` or move the definition to a `let` statement just above:
+You cannot add a `: TYPE` because it's invalid syntax in this position. Instead, you can move the definition to a `let` statement just above:
 
 ```svelte
 <script lang="ts">
 	let count = 0;
 
-	$: option1 = (count * 2) as number;
-
-	let option2: number;
-	$: option2 = count * 2;
+	let doubled: number;
+	$: doubled = count * 2;
 </script>
 ```