[components] Revert "Closes https://github.com/mozilla-mobile/android-components/issues/8693: Integrate GeckoWebExecutor#FETCH_FLAG_PRIVATE."

This reverts commit 7f97412251cbec11a371fce1652ad7a760184d93.

mobile/android/android-components/components/lib/fetch-okhttp/src/main/java/mozilla/components/lib/fetch/okhttp/OkHttpClient.kt

@@ -37,10 +37,6 @@ class OkHttpClient(
     )
 
     override fun fetch(request: Request): Response {
-        if (request.private) {
-            throw IllegalArgumentException("Client doesn't support private request")
-        }
-
         if (request.isDataUri()) {
             return fetchDataUri(request)
         }