Fixes #1637

Also fixes some other bugs and inconsistencies in our handling of prune previous:

• update, delete with a date_range, and defragment_symbol_data also did not respect the prune previous lib config setting/env var.
• delete with a date_range argument and defragment_symbol_data used prune_previous_versions (i.e. with a trailing s). All other methods use prune_previous_version (i.e. without the trailing s). For backwards compatibility, these two methods now support both variants.
• write_metadata and delete_data_in_range on the V2 API did not have a prune_previous_versions argument.
• write_metadata_batch on the V2 API defaulted the argument to None (implying respecting the lib config setting, but this is not a library option on the V2 API), where everything else defaults to False.
• Homogenised docstrings for prune_previous_versions on V2 API.