Refactor TranscriptProcessor into user and assistant processors

src/pipecat/frames/frames.py

@@ -207,13 +207,6 @@ class InterimTranscriptionFrame(TextFrame):
         return f"{self.name}(user: {self.user_id}, text: [{self.text}], language: {self.language}, timestamp: {self.timestamp})"
 
 
-@dataclass
-class OpenAILLMContextUserTimestampFrame(DataFrame):
-    """Timestamp information for user message in LLM context."""
-
-    timestamp: str
-
-
 @dataclass
 class OpenAILLMContextAssistantTimestampFrame(DataFrame):
     """Timestamp information for assistant message in LLM context."""