Revert last canary flag PR and use a better method (#5535)

* Revert "Implement Labrinth Canary API flag (#5531)"

This reverts commit 3b21944a75.

* Use Labrinth-Canary header instead of cookie for API canary

* prepr

* fix rebase

apps/frontend/src/helpers/canary.ts

@@ -0,0 +1,15 @@
+export const LABRINTH_CANARY_HEADER = 'Labrinth-Canary'
+export const LABRINTH_CANARY_VALUE = 'always'
+
+export function withLabrinthCanaryHeader(headers: Record<string, string> = {}) {
+	const flags = useFeatureFlags()
+
+	if (!flags.value.labrinthApiCanary) {
+		return headers
+	}
+
+	return {
+		...headers,
+		[LABRINTH_CANARY_HEADER]: LABRINTH_CANARY_VALUE,
+	}
+}