Remove references to HebrewCalendar

[SLaks]

This is a followup of hebcal/hebcal-es6#475

I want to be able to call leyning APIs without bringing 150KB+ of Zmanim code into my bundle.

This means that, after I split APIs out of HebrewCalendar, I must migrate all references to HebrewCalendar in this repo.

This includes:

• Change HebrewCalendar.getSedra() to call a standalone export (easy)
• Handle HebrewCalendar.getHolidaysOnDate(); TBD based on Refactor to work with Tree Shaking hebcal-es6#475
• Optional, breaking change: Move csv.ts out of index.ts, so it's only imported if actually referenced.
  • Tree shaking should drop it anyway, so this may not be necessary.
  • It would let me https://github.com/SLaks/tikkun.io/blob/calendar-rewrite-full/src/calendar-model/hacks.d.ts