Re #7656. Remove test of BASIS loading.

This is now covered by the LoadLotsOfFiles system test (via the addition
of an 'expected' file to check the number of events in the first
event list).
Re #7656. Try to make the slowest test method faster.

By only loading one bank.
Re #7656. Remove test that's been replaced by a system test.

Note that this test wasn't testing what it purported to because lines
235 & 280 were identical! When this error was fixed the test failed
(the reason for which has been addressed in the new system test).
Re #7656. Consolidate some of the test methods.

This means that the algorithm is run fewer times, but the same things
are still tested.
Also don't load the logs where possible.
Re #7656. Fix copy-paste error.
Merge remote branch 'origin/feature/7656_speed_up_loadeventnexustest'