remove LLMResponseStartFrame and LLMResponseEndFrame

This was added in the past to properly handle interruptions for the
LLMAssistantContextAggregator. But this is not necessary anymore since we can
handle interruptions by just processing the StartInterruptionFrame, so there's
no need for these extra frames.

CHANGELOG.md

@@ -5,6 +5,17 @@ All notable changes to **pipecat** will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Removed
+
+- We remove the `LLMResponseStartFrame` and `LLMResponseEndFrame` frames. These
+  were added in the past to properly handle interruptions for the
+  `LLMAssistantContextAggregator`. But the `LLMContextAggregator` is now based
+  on `LLMResponseAggregator` which handles interruptions properly by just
+  processing the `StartInterruptionFrame`, so there's no need for these extra
+  frames any more.
+
 ## [0.0.36] - 2024-07-02
 
 ### Added