[XLA:GPU] Stop passing `stream` to methods of `GpuConvAlgorithmPicker`.
[XLA:GPU] Stop passing `stream` to methods of `GpuConvAlgorithmPicker`.

The `stream` always comes from the `config_` field. Passing it around, as opposed to directly reading it from the field is confusing as it gives the wrong impression that it may be different than what is stored in the `config_`.
