Revert Uri class due to bug 39710

Revert Uri class due to bug 39710

Revert 94f623363beb00a7a211e8f8f1f39bc12b4713ed. Apparently all
ReverseChronologicalPager subclasses were broken by the unexplained
interface change in wfArrayToCgi(): changing the interpretation of
null array values from "omit this key" to "include this key with no
value". The function has always been called with the former
interpretation, that's why the special case was in there.

Also reverted dependent changes 4b517fa and part of 3d97704.

Change-Id: I41dadbde5d0e0e4c54cc76bfc13c263c15c73828