Remove limits on mw.language:formatDate()

Remove the 6000 character per page limit of mw.language:formatDate(). It
only exists because ParserFunctions has something like it for performance
reasons. Since Lua has a maximum execution time, there's no reason that it
needs this as well.

Change-Id: I42ae4f51295135007c6e2edc66ec36b7d96e3be3
Merge "Remove limits on mw.language:formatDate()"