unstructured

086b8d6f - rfctr(part): prepare for pluggable auto-partitioners 2 (#3657)

rfctr(part): prepare for pluggable auto-partitioners 2 (#3657) **Summary** Step 2 in prep for pluggable auto-partitioners, remove `regex_metadata` field from `ElementMetadata`. **Additional Context** - "regex-metadata" was an experimental feature that didn't pan out. - It's implemented by one of the post-partitioning metadata decorators, so get rid of it as part of the cleanup before consolidating those decorators.