Revert "libaudiohal@aidl: Make IHalAdapterVendorExtension mandatory"

Revert submission 2929484-fix-b-321651892-ihaladapter

Reason for revert: possible cause of b/323385784

Reverted changes: /q/submissionid:2929484-fix-b-321651892-ihaladapter

Change-Id: Ifaafeec27bee08648a3ced6d507b99454c317692
diff --git a/media/libaudiohal/impl/DevicesFactoryHalAidl.h b/media/libaudiohal/impl/DevicesFactoryHalAidl.h
index 2a3a9e7..17bfe43 100644
--- a/media/libaudiohal/impl/DevicesFactoryHalAidl.h
+++ b/media/libaudiohal/impl/DevicesFactoryHalAidl.h
@@ -45,7 +45,10 @@
 
   private:
     const std::shared_ptr<::aidl::android::hardware::audio::core::IConfig> mConfig;
-    const std::shared_ptr<::aidl::android::media::audio::IHalAdapterVendorExtension> mVendorExt;
+    std::optional<std::shared_ptr<::aidl::android::media::audio::IHalAdapterVendorExtension>>
+            mVendorExt;
+
+    std::shared_ptr<::aidl::android::media::audio::IHalAdapterVendorExtension> getVendorExtension();
 
     ~DevicesFactoryHalAidl() = default;
 };