As of WT-4427, WiredTiger no longer supports anything other than 8B timestamps, which makes the hexadecimal string APIs for getting/setting timestamps unnecessary overhead.

daniel.gottlieb and geert.bosch have expressed a preference for making the switch, noting the string conversions to/from MongoDB's internal integral timestamp values do show up on performance profiles.

Change the WiredTiger timestamp APIs to use integral values instead of hexadecimal strings.

cc: sue.loverso