fix(ace-step): drop nonexistent Get* proto accessors in SoundGeneration (#11069) (#11072)

The Python gRPC bindings expose message fields as plain attributes
(request.language, request.caption), not Go/Java-style Get*() accessors.
Because request.language is an empty string when unset, the

    request.language or request.GetLanguage() or "en"

expression falls through to request.GetLanguage(), which does not exist
on the generated Python message and raises AttributeError, surfaced to
clients as:

    rpc error: code = Unknown desc = Exception calling application: GetLanguage

Every /v1/sound-generation request without an explicit language field
failed. Drop the bogus accessor calls (TTS already uses the plain-field
form a few lines below).

Signed-off-by: Tai An <antai12232931@outlook.com>

backend/python/ace-step/backend.py

@@ -401,16 +401,16 @@ class BackendServicer(backend_pb2_grpc.BackendServicer):
                 "sample_query": request.text or "",
                 "sample_mode": True,
                 "thinking": True,
-                "vocal_language": request.language or request.GetLanguage() or "en",
+                "vocal_language": request.language or "en",
                 "instrumental": request.instrumental if request.HasField("instrumental") else False,
             }
         else:
-            caption = request.caption or request.GetCaption() or request.text
+            caption = request.caption or request.text
             payload = {
                 "prompt": caption,
                 "lyrics": request.lyrics or request.lyrics or "",
                 "thinking": request.think if request.HasField("think") else False,
-                "vocal_language": request.language or request.GetLanguage() or "en",
+                "vocal_language": request.language or "en",
             }
             if request.HasField("bpm"):
                 payload["bpm"] = request.bpm