There are now only two renderers (only generic over the GL context)
- `AutoRenderer` which is both the old `OwningRenderer` and also
sets up a `SimpleTextureMap` automatically
- `Renderer` which borrows both the GL context and the texture map
on every call to Render
This means the `RendererBuilder` can be entirely removed.
Also `TrivialTextureMap` renamed to `SimpleTextureMap`.