tests: Don't change settings.STATIC_URL in the XML-RPC tests

tests: Don't change settings.STATIC_URL in the XML-RPC tests

I tracked down a weird bug where the Selenium tests supposed to serve
all static files (.css, .js. ...) weren't doing so when running the
full test suite, but everything was working when running the tests in
isolation.

Turns out one of the other tests was changing settings.STATIC_URL
mid-way without restoring the original value in tearDown() and thus
impacting other tests.

It seems that this change wasn't necessary, the XML-RPC server doesn't
server any static file anyway.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Acked-by: Stephen Finucane <stephen.finucane@intel.com>