hgweb: remove unused second argument of nextPageVarGet()
nextPageVarGet is a function that's used in ajaxScrollInit() to produce URL of
the next page. Before
f84b01257e06, its second argument previousVal was a
number on /graph pages, and the code was simply adding 60 to it and returning
the resulting value. Now previousVal can only be a string containing changeset
hash, which can't be used the same way (and in fact isn't used in any way).
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.