Remove rc_cur_time attribute in client

rc_cur_time attribute has been removed from recent changes (I4a9c2fa8),
and before that was unused. As well, the column might be dropped from
the recentchanges table. (see I48989ace)

No reason at all for having the attribute in Wikibase recent
changes entries.

Change-Id: Ia5a85703ddefb1256e2e7acd78c7bbc060887f12
Merge "Remove rc_cur_time attribute in client"