do not craft our own api url

mediawiki.api.js is now smart enough to do this properly.

the only reason we used to craft our own url here is because
mediawiki.api.js got its start inside UploadWizard. But,
if we create our API url this way, it can mess up Selenium
testing on Vagrant due to mismatches of port numbers

Change-Id: Iac25239cf240934bd1e3ce349c05f1b41eb23b8c