Remove SubmitHistoryDatespanFilter and fallback to SubmitHistoryReport behavior

http://manage.dimagi.com/default.asp?141639
Actually I'm just deleting this separate filter altogether, turns out it's not necessary, as the SubmitHistoryReport already uses oldest form submission as a default daterange, as defined here:
https://github.com/dimagi/commcare-hq/blob/submit-history-filter/corehq/apps/reports/standard/inspect.py#L87-L89, which references
https://github.com/dimagi/commcare-hq/blob/submit-history-filter/corehq/apps/reports/util.py#L477-L498