Remove S03 beamline and 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 (but maybe not, see first comment in this issue)
• The @pytest.mark.s03 marker is changed to a more meaningful name for the remaining system tests
• All devices annotated with skip=BL == s03 are no longer annotated with skip
• i03.py has BL = get_beamline_name("i03") instead of s03 and there is no mention of s03 anywhere

[olliesilvester]

@rtuck99 I seem to remember there are a few tests which say @pytest.mark.s03 but don't actually have anything to do with s03 - we just marked it with that as the tests don't pass locally for some other reason. So we should be a bit careful to not just remove all the s03 tests without checking