feat: remove legacy library from homepage (#155)

It's been a while the portal is online and people are already aware of
the new libraries. We still have the banner on top of the page that can
help people knowing about the new library and the upgrade guide.

Author: ilbertt

docs/src/content/docs/index.mdx

@@ -32,23 +32,6 @@ import { Card, CardGrid, LinkButton } from "@astrojs/starlight/components";
         </div>
     </Card>
 
-    <Card title="Agent JS (Legacy)">
-        The <code>@dfinity/agent</code> and related packages are no longer actively
-        maintained. Please migrate to the new <code>@icp-sdk/core</code>
-        package.
-
-        <div>
-            <LinkButton
-                href="/core/v3.2"
-                variant="minimal"
-                icon="right-caret"
-                iconPlacement="start"
-            >
-                View legacy <code class="dfn-text-highlight">@dfinity/agent</code> docs
-            </LinkButton>
-        </div>
-    </Card>
-
     <Card title="ICP JS SDK Auth">
         Authenticate users on ICP web apps.