Error for fetching non-local files

[samuelbray32]

• This line was added to fetch_nwb as part of the custom AnalysisNwbfile tables PR
  

  spyglass/src/spyglass/utils/dj_helper_fn.py

  Line 365 in 32b6950

  attrs = list(attrs) + ["nwb2load_filepath"]

• Fetching this attribute requires accessing through the externals table
• Raises an error for dandi-loaded files which don't exist locally

solution

• Previously this was only fetched for non-dandi files
• The value of this key is getting overwritten within the following loop here anyways
• I think we could just skip the fetch caused by the error line above

@CBroz1 , there's a comment at the line I mentioned that it solves an error for the custom tables. Do you know if there's some reason I'm missing that it's still necessary

[CBroz1]

I do not recall the specifics of the error this raised with a custom analysis table, sorry. Just that I couldn't fetch from an nwb from a custom table during development. If that now works, it's probably safe to remove

In general, this function is suffering from some bloat that could probably be folded into the class hierarchy - even if that meant removing support for non SpyglassMixin tables