Don't process history entries outside date range

The following queries cut the number of queries in half for a busy week:

- Remove skip() method from events class since history api does the filtering.
- When processing history events for an issue, only process ones within desired
time range.

Before:
- Total queries executed: 1232
- Unique queries executed: 1231
- Total query execution time: 0.7097 seconds

After:
- Total queries executed: 574
- Unique queries executed: 573
- Total query execution time: 0.2581 seconds

Issue #17966
Yes, I actually checked the index while writing the code, but didn't do it in the query, since it is more complex to handle case where both are null or one is null but not the other.  Then I forgot to go back and change the query.  Will do.