Make Developer Guide sidebar button an external link

Author: GDYendell

backstage/packages/app/src/App.tsx

@@ -32,7 +32,6 @@ import { Route } from 'react-router-dom';
 import { apis } from './apis';
 import { Root } from './components/Root';
 import { entityPage } from './components/catalog/EntityPage';
-import { DeveloperGuidePage } from './components/dev-guide/GuideDocsPage';
 import { HomePage } from './components/home/HomePage';
 import { PortalDocsPage } from './components/portal-docs/PortalDocsPage';
 import { searchPage } from './components/search/SearchPage';
@@ -63,7 +62,6 @@ const routes = (
       <HomePage />
     </Route>
     <Route path="/catalog" element={<CatalogIndexPage />} />
-    <Route path="/guide" element={<DeveloperGuidePage />} />
     <Route path="/portal-docs" element={<PortalDocsPage />} />
     <Route
       path="/catalog/:namespace/:kind/:name"

backstage/packages/app/src/components/Root/Root.tsx

@@ -68,7 +68,7 @@ export const Root = ({ children }: PropsWithChildren<{}>) => (
         <SidebarItem icon={CategoryIcon} to="/catalog" text="Catalog" />
         <SidebarItem
           icon={LibraryBooksIcon}
-          to="/guide"
+          to="https://dev-guide.diamond.ac.uk"
           text="Developer Guide"
         />
         {/* End global nav */}