How can I know why a DLL is being imported in my build?

Unity Engine
1

I’m trying to get rid of a specific DLL in my build when being compiled on a specific platform. I already used conditional compiler flags in code to make sure it’s not being used in code

#if !UNITY_IOS
using WebSocketSharp;
#endif

But I’m still seeing in the Editor.log that NativeWebSocket.dll is being used.

I’m also worried that it might be a dependency from some other 3rd party library, so how can I know who is using that DLL and how can I get rid of it if it’s on a 3rd party library?

Thank you!