Remove cwd path for nft_metadata_cache setting

[trepca]

This is no different than our other big stuff. It need not be defaulted differently here. Using ./ just means it will go any number of places depending what directory the user is in when they run chia.

Originally posted by @altendky in https://github.com/Chia-Network/chia-blockchain/pull/13018#discussion_r964005327