stream: Remove "simple" stream API
The simple stream API is a way to create a stream from just a mainloop. Context and Core are handled automatically internally.
Accomodating this API severely complicates the code for our rust bindings, making them messy and much bigger.
Since the simple API only saves a couple lines for creating a context and core, its benefit is not very much, so this commit removes the simple API and simplifies the stream code.