Remove unnecessary org mode headers and properties in prompts to send

[aGolduck]

Org mode headers and properties are sent in promts, they seemed unnecessary, for example, this is a request body

{
  "model": "gpt-4",
  "messages": [
    {
      "role": "system",
      "content": "You are a large language model living in Emacs and a helpful assistant."
    },
    {
      "role": "user",
      "content": "* another test\n:PROPERTIES:\n:GPTEL_TOPIC: another-test\n:END:\n\n** this is a test"
    }
  ],
  "stream": true,
  "temperature": 1.0
}

[karthink]

Thanks for the suggestion -- this is a frequent one! See #141 and many discussions in the discussions page.

This is a low-medium priority issue for me right now as it's basically harmless, except for the negligible token cost of few dozen extra tokens. There are several semi-broken things I need to fix first -- I'll get to this eventually.