Remove a set of one-time-use assets

We used these files when initially creating the new L2s/L3s, but they're
now out of date. We've made subsequent changes directly to
all_fields.tsv, which is now at the top of our workflow for updating
field text. So for clarity I'm removing these assets, because they contain
information that's *almost* the same as in field_meta.

I'm putting the notebook I used to create an updated version of
field_meta.jsonl that incorporates our final decisions from
l2_revisions.xlsx in an analysis subdirectory.