Drop native offline chat support with llama-cpp-python

It is recommended to chat with open-source models by running an
open-source server like Ollama, Llama.cpp on your GPU powered machine
or use a commercial provider of open-source models like DeepInfra or
OpenRouter.

These chat model serving options provide a mature Openai compatible
API that already works with Khoj.

Directly using offline chat models only worked reasonably with pip
install on a machine with GPU. Docker setup of khoj had trouble with
accessing GPU. And without GPU access offline chat is too slow.

Deprecating support for an offline chat provider directly from within
Khoj will reduce code complexity and increase developement velocity.
Offline models are subsumed to use existing Openai ai model provider.

.github/workflows/test.yml

@@ -64,8 +64,6 @@ jobs:
           DEBIAN_FRONTEND: noninteractive
         run: |
           apt update && apt install -y git libegl1 sqlite3 libsqlite3-dev libsqlite3-0 ffmpeg libsm6 libxext6
-          # required by llama-cpp-python prebuilt wheels
-          apt install -y musl-dev && ln -s /usr/lib/x86_64-linux-musl/libc.so /lib/libc.musl-x86_64.so.1
 
       - name: ⬇️ Install Postgres
         env: