Replace all "setQueryParam()" calls with "remove/replaceQueryParam()"

Summary: Ref T13250. See D20149. Mostly: clarify semantics. Partly: remove magic "null" behavior.

Test Plan: Poked around, but mostly just inspection since these are pretty much one-for-one.

Reviewers: amckinley

Reviewed By: amckinley

Subscribers: yelirekim

Maniphest Tasks: T13250

Differential Revision: https://secure.phabricator.com/D20154