[MDX] Remove `frontmatterOptions` (#4204)

* feat: remove frontmatterOptions config

* test: remove custom frontmatter suite

* deps: remove remark-mdx-frontmatter

* docs: remove `frontmatterOptions` config

* chore: changeset

1 files changed, 0 insertions, 17 deletions

diff --git a/packages/integrations/mdx/test/mdx-frontmatter.test.js b/packages/integrations/mdx/test/mdx-frontmatter.test.js
index 5f0316986..e69919bd5 100644
--- a/packages/integrations/mdx/test/mdx-frontmatter.test.js
+++ b/packages/integrations/mdx/test/mdx-frontmatter.test.js
@@ -56,21 +56,4 @@ describe('MDX frontmatter', () => {
 		expect(headingSlugs).to.contain('section-1');
 		expect(headingSlugs).to.contain('section-2');
 	});
-
-	it('extracts frontmatter to "customFrontmatter" export when configured', async () => {
-		const customFixture = await loadFixture({
-			root: new URL('./fixtures/mdx-custom-frontmatter-name/', import.meta.url),
-			integrations: [
-				mdx({
-					frontmatterOptions: {
-						name: 'customFrontmatter',
-					},
-				}),
-			],
-		});
-		await customFixture.build();
-
-		const { titles } = JSON.parse(await customFixture.readFile('/glob.json'));
-		expect(titles).to.include('Using YAML frontmatter');
-	});
 });