Remove dead import

src/chatdbg/chatdbg_utils.py

@@ -55,8 +55,6 @@ def read_lines(file_path: str, start_line: int, end_line: int) -> str:
 
 
 def explain(source_code: str, traceback: str, exception: str, really_run=True) -> None:
-    import httpx
-
     user_prompt = "Explain what the root cause of this error is, given the following source code context for each stack frame and a traceback, and propose a fix. In your response, never refer to the frames given below (as in, 'frame 0'). Instead, always refer only to specific lines and filenames of source code.\n"
     user_prompt += "\n"
     user_prompt += "Source code for each stack frame:\n```\n"