Remove reliance on ENV file

[Yiannis128]

Environment file loading should be discarded, and instead the variables should be loaded directly from the system environment. The current system is too complicated:

Environment variables are loaded in the following order:

1. Environment variables already loaded. Any variable not present will be looked for in
.env files in the following locations.
2. .env file in the current directory, moving upwards in the directory tree.
3. esbmc-ai.env file in the current directory, moving upwards in the directory tree.
4. esbmc-ai.env file in $HOME/.config/ for Linux/macOS and %userprofile% for Windows.