uncommit: drop the hyphen from --current-user and --current-date
I didn't pay enough attention to these long forms- graft, amend and MQ already
use the old style naming. It's probably more important to be consistent than
modern. The hypenated style came from evolve.
Yuya mentioned this naming discrepancy in 4145fd3569c3, but it didn't attract
any discussion. There's also a bit of inconsistency in that the default
parameter for currentdate is False for graft, and None for the rest.
Differential Revision: https://phab.mercurial-scm.org/D6841