Stop stubbing an imminence data set URL in all tests
Stop stubbing an imminence data set URL in all tests

Removing the stub doesn't seem to cause a problem and it looks like this
stub hasn't been needed since 2011 (see:
b3e0c8aefa2cb3b6c85d67c384f31dcb746ff268).

alphagov/panopticon,alphagov/panopticon,alphagov/panopticon,alphagov/panopticon