Optimisation: Avoid unnecessary duplicate call to expensive get_repo_map() method

[Finndersen]

Coder calls self.get_repo_map() in get_chat_files_messages() just to determine whether the repo map is included in the prompt.
This is an expensive method and is already called immediately before get_chat_files_messages(), so that information can just be provided as an argument for efficiency.

[paul-gauthier]

Thanks for your interest in aider and for putting together this PR.

The repo map call should be cached, so wouldn't only be slow if it needs to be recomputed.

[Finndersen]

On but it still looks like there's a decent amount of code path before the cache will even be hit, so I still think this is a worthy optimisation seeing as this information will always be available before the method is called