Remove second link to Sourcegraph Model Provider from sidebar (#1418)

In two places, this looks weird in the sidebar.

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Author: eseliger

src/data/navigation.ts

@@ -241,10 +241,6 @@ export const navigation: NavigationItem[] = [
 								title: 'Prompts Guide',
 								href: '/cody/prompts-guide'
 							},
-							{
-								title: 'Sourcegraph Model Provider',
-								href: '/model-provider'
-							},
 							{
 								title: 'Enterprise Architecture',
 								href: '/cody/core-concepts/enterprise-architecture'