[Code Cleanup] Cleanup type for auto_session_last_session_dir in code

[devansh08]

Not really a bug, just a code cleanup suggestion :)

In this file, the type for auto_session_last_session_dir is still present even though the config is not actively being used in the codebase. Only reference of it is here and is commented.

Would be great if this could be commented or removed, as it just shows up as a Lua diagnostic warning mentioning a missing field.

PS: I realise I've messed up the issue template for this, but this was not really a bug. Also, I was not sure if this code was a WIP or something that is not required (and was missed to be cleaned up), so couldn't decide what to even raise a PR for (to comment or to remove). Apologies :)