Remove system tests which require S03

[olliesilvester]

As discussed in #183, we think the overhead required to use and maintain the system tests which need S03 is too high, and they haven't been working for a long time. We currently ignore the results of the daily system tests because of this, so we are better off without them

Acceptance Criteria

• System tests which require S03 are identified and removed. Note that this isn't every test which has @pytest.mark.s03
• The @pytest.mark.s03 marker is changed to a more meaningful name for the remaining system tests