rfctr(pptx): minify HTML and table.text is cct (#3734)
**Summary**
Eliminate historical "idiosyncracies" of `table.metadata.text_as_html`
HTML introduced by `partition_pptx()`. Produce minified `.text_as_html`
consistent with that formed by chunking.
**Additional Context**
- PPTX `.metadata.text_as_html` is minified (no extra whitespace or
thead, tbody, tfoot elements).
- `table.text` is clean-concatenated-text (CCT) of table.
- Last use of `tabulate` library is removed and that dependency is
removed from `base.in`.
