resourceloader: Don't call wfExpandUrl() on load.php urls
wfExpandUrl() should only be used if the url needs to be absolute
and/or needs to point to the canonical, internal or default wgServer
for the wiki.
For meta-data or API responses this can make sense, but for resources
loaded by the browser from the current page, there is no added value
in expanding these to the default domain.
This is causing problems in custom setups such as at Wikimedia,
with "zero" and "m" sub domains for which $wgServer points to the