LLMUserContextAggregator: don't reset timer with interim transcription

It turns out that in some cases we only get interim transcriptions (e.g. someone
is speaking very very softly or someone is talking in the background). In those
cases we don't want to interrupt the bot because there's really nothing to
interrupt the bot for.

We originally thought we should interrupt the bot right at the time we got an
interim frame, but this is causing too many false positives. It's actually
better to simply wait for a real transcription before interrupting (in case VAD
didn't interrupt).

src/pipecat/processors/aggregators/llm_response.py

@@ -301,8 +301,6 @@ class LLMUserContextAggregator(LLMContextResponseAggregator):
 
     async def _handle_interim_transcription(self, _: InterimTranscriptionFrame):
         self._seen_interim_results = True
-        # Reset aggregation timer.
-        self._aggregation_event.set()
 
     def _create_aggregation_task(self):
         self._aggregation_task = self.create_task(self._aggregation_task_handler())