Fix link for using declaration

Author: guardrex

aspnetcore/blazor/call-web-api.md

@@ -358,7 +358,7 @@ The solution includes a demonstration of obtaining weather data securely via an
 
 ## Disposal of `HttpRequestMessage`, `HttpResponseMessage`, and `HttpClient`
 
-An <xref:System.Net.Http.HttpRequestMessage> without a body doesn't require explicit disposal with a [`using` declaration (C# 8 or later)](/dotnet/csharp/language-reference/proposals/csharp-8.0/using) or a [`using` block (all C# releases)](/dotnet/csharp/language-reference/keywords/using), but we recommend disposing with every use for the following reasons:
+An <xref:System.Net.Http.HttpRequestMessage> without a body doesn't require explicit disposal with a [`using` declaration (C# 8 or later)](/dotnet/csharp/language-reference/keywords/using-directive) or a [`using` block (all C# releases)](/dotnet/csharp/language-reference/keywords/using), but we recommend disposing with every use for the following reasons:
 
 * To gain a performance improvement by avoiding finalizers.
 * It hardens the code for the future in case a request body is ever added to an <xref:System.Net.Http.HttpRequestMessage> that didn't initially have one.