decoder/Client: add OpenUri(), replacing decoder_open_uri()

src/decoder/DecoderAPI.hxx

@@ -54,16 +54,6 @@ class DecoderClient;
  */
 class StopDecoder {};
 
-/**
- * Open a new #InputStream and wait until it's ready.
- *
- * Throws #StopDecoder if DecoderCommand::STOP was received.
- *
- * Throws std::runtime_error on error.
- */
-InputStreamPtr
-decoder_open_uri(DecoderClient &decoder, const char *uri);
-
 /**
  * Blocking read from the input stream.
  *